IT WAS a quickie trip to Europe. They took the Concorde to London, checked into the Portman Hotel for four says, jetted to Paris for three nights at the Plaza Athenee and much feasting.

And? "And you can't believe what it cost," said the family treasurer.

I can believe. I can't do it, but I can believe it. After all, when you have recently tried and failed to get a single motel room near Miami airport for less than $40, you are persuaded to accept all sorts of lunatic developments.

On the other hand, when you're thinking in practical terms of your own trip to Europe, there are statements it pays to question. Some things you hear, unfortunately, are too good to be true, and others reflect situations that don't have to be. For instance:

"Paris is pretty, but you can't afford to go for a look." Not many can if it means taking the Concorde, but you can get clean, pleasant hotel rooms in Paris for $40 or $50 double; eat tolerably well for $15 a head with wine, taxes and tips included; take 50 cents a trip; sightsee practically forever for free. Those are the ingredients of a "low-budget" trip quite a few cuts above rock-bottom but not in the care-free category.

That means that, yes you may feel pinched if you have in mind dining in gastronomic palaces like Lasserre ($50 to $100 per person is what such spots will set you back), taking in the dinner show at the Lido (count on at least $60), buying a handbag at Chanel (would you believe $600?) or going disco at Le Palace (oh, never mind!)

To find the good things at the lower end of the rainbow? The just-published "Let's Go: the Budget Guide to France" ($4.95 at most bookstores) is aimed at students but useful to anyone, and "A Touch of Paris," a quarterly guide on sale at most tourist-area newsstands in Paris, is as good at name-dropping (who has what for how much?) as anything you could hope to find.

"Greece is great but just too crowded." What most people who say that mean is that Athens and the islands of Mykonos, Ios, Skiathos, Kos, Samos, Paxi, Poros, Aegina, Spetse, Hydra, Santorini, Crete and Corfu -- among others -- just about burst their buttons in July and August. Because Poros, Aegina and Spetse are favored by Athenian weekenders, you can still swing your arms and not hit someone if you go midweek. Mykonos, Hydra and Skiathos, on the other hand, are the international outposts and Most Likely to Be Overrun. And then some.

Of course, lots of people like lots of people, especially the under-30s crowd that now makes up about three-quarters of the summer mob. What they may not like are the jellyfish that have been showing up around the northermost islands and the heat that bakes Athens dry during this same period.

If you're not going for the action, earlier and later are infinitely better times to visit, especially if you want to hop from one place to another. Along with everything else, there are awesome transportation jams in high season. And from mid-June through September, this is no place to show up without a confirmed room reservation -- unless, of course, you don't mind a full-day search and maybe a mattress on a rooftop.

"Scandinavia is beginning to look affordable." If you give up drinking (or import your own) and intend to diet, you can probably manage one day in Copenhagen or Stockholm for what two days would cost you in Lisbon this summer. Because food is so expensive, a barebones budget is a little too painful, but someone ready to put out $60 for a hotel room in the United States this year won't find Denmark, Sweden, Norway or Finland that far out of line.

Furthermore, there are concessions -- principally a hotel voucher plan in Sweden that offers twin-bedded rooms for two at more than 400 hotels for $26 or $17 per night per person, breakfast included. The Scandinavian National Tourist office at 75 Rockefeller Plaza, New York, N.Y. 10019, can give details on things like tourist menu plans ($5.35 at some 400 Swedish restaurants), transportation passes, special three-night-stay arrangements, inexpensive farm and cottage accommodations, and more.

"Spain is always attractive, but they've been throwing bombs." Last summer, Basque separatists did indeed target tourists, and although their fight for autonomy continues, they seem to have switched to killing police and soliders. Since certain governmental changes have been won, it is believe that some steam has been let out of the movement. The U.S. State Department "certainly doesn't recommend against going," a spokesman says, and there seems to be no reason for undue concern. The Spanish government has reportedly beefed up security at beaches and transportation terminals in particular.

"Hotel prices in Vienna are out of sight." Look again. Compared with U.S. hotel prices, the ones in Europe's big cities don't look quite so crushing. For instance: Although doubles go as high as $150, a single person who moved early enough to catch one of the minimum-rate rooms at the esteemed Sacher Hotel could enjoy Old World luxury (on a small-footage basis) for approximately $51 a night.

Vienna especially has excellent "pensions," bed-and-breakfast places that are really as large and as well-equipped as many small hotels. Furthermore, they have a generally high standard of cleanliness. While they're slightly more expensive than their counterparts in many other European cities, you do get what you pay for. At the Pension Zipser, 8 Langegasse, for instance, an attractive but simple single or double room this summer will cost $22 to $25 per person. There are room telephones and an elevator, private bathrooms with well-scrubbed modern showers, a lobby lounge with some of the easiest drink prices in the city and a cordial staff.

Make no mistake, Vienna is no little spender's delight. But you can manage better than you think if you stay somewhere central like the Zipser, avoid taxis, grab the public transit map handed out at tourist information centers and try to live like a student prince -- with the accent on student.

"Real students can save a bundle in Amsterdam by staying at student hotels." Similar to hostels but without all the rules, student hotels with bunk beds in dorm rooms are priced about right: $5 to $7 per person. But if you're a cleanliness freak or even halfway close, have a look before you sign up. Some of the places lack. A lot. You might, too, in the end; reportedly there's a high ripoff rate, even tales of lockers being attacked with blunt instruments.

Amsterdam itself is very hospitable to young travelers, and the city even publishes a tip sheet called "Use It," with all kinds of leads to getting around on the cheap.