You can do some things to your without tools, but this is pretty much restricted to inspecting for leaks, loose or worn parts and so on.
If you're really going to work on your car - do oil changes or tuneups, change belts and hoses and so on - you'll need tools. But the price range of tools can vary tremendously. For example, a timing light in one store might by $10.95; in another store it's $50.
Which one should you buy? Do you need the kind of tools professional mechanics use, or will the ones you can buy at your local hardware store work okay?
Usually the tools bought by mechanics in garages are more expensive than those available in stores for the public. That higher price often pays for equipment that is sturdier.
A professional mechanic uses some tools more in a month than the average person does in several years. Take a dwell-tach, for example. Some pros will use this instrument more in five days than you ever will.
So the pro's tools have to be rugged. Do-it-yourselfers can find perfectly acceptable tools in the mass-merchandise stores.
That doesn't mean the tools you get are doomed to a short life: Most tools readily available to the consumer will last a lifetime with reasonable care, which means using tools for the purposes they were made and storing them properly. You can't expect a timing light to survive being run over by a wheel because you forgot to pick it up. And you can't blame an adjustable wrench that becomes a useless piece of rust because you left it in the yard for three months.
Nor does it mean you should simply buy the cheapest tools you can find: If you see a bag of 20 wrenches on sale for $1.98, you can bet they're not of superior quality. When I was kid I bought a selection of Phillips screwdrivers for a few cents; I thought I was getting a good deal. I had those screwdrivers for years - I never did find a Phillips screw any of them would fit.
Still, if you're on a tight budget, cheap wrenches may be better than nothing. But if one of them breaks the first time you try to loosen a stubborn nut or bolt, don't be surprises.
On the other hand, if a Craftsman wrench ever breaks (Craftsman tools are sold by Sears), just take it back and you'll get a new one, no questions asked. J.C. Penney also has the same guarantee on its wrenches.
Wrenches and screwdrivers are the tools you'll probably use the most. Buy quality here.
As for test instruments, generally speaking the instruments available to the public, even the cheap ones, are accurate enough for the do-it-yourselfer. The face of a $12 dwell-tach you picked up at the local discount store may be smaller and harder to read than the one that's part of the pro's fancy $4,000 engine analyzer. But it's probably accurate enough for your purposes. As long as you treat it right, it'll last a long time.
One place where there's a big difference - in cost and ruggedness - is in jack stands, needed for a lot of auto-repair jobs. For example, where I live a pair of jack stands in the auto department of a local store is $16 - rated at two tons (each stand is supposed to be able to support 4,000 pounds).
On the other hand, a set of professional stands rated at two tons is $52. They're visibly more rugged, have a wider support base and inspire greater confidence.
Still, if the cheaper stands are used properly, and their weight limit rating isn't exceeded, they should provide you with safe and adequate service.