Every month the editors of Washington Consumers' Checkbook magazine report here some of the best prices they have found in surveying more than 300 area retailers.

The retailers have promised to hold these prices -- and offer rainchecks if supply runs out -- until Aug. 31. It's a good idea to call ahead to check that a product is in stock. Stores may limit purchases to one per customer.

Here's a partial listing of bargain prices based on Washington Consumers' Checkbook magazine surveys. TURNTABLES

Yamaha P-520 turntable, fully automatic -- $179 at Audio Associates, Laurel (953-7242), Langley Park (434-4740), Arlington (525-1889), Bethesda (530-6003), Springfield (971-1060).

Sansui P-L35 turntable, fully automatic -- $138 at Paul's Audio Video Center, Vienna (827-5797).

Dual CS620 turntable, fully automatic -- $199 at Audio Buys, Bailey's Crossroads (578-3033). WASHING MACHINES

Whirlpool washing machine, model LA7800XM, 6 cycles -- $380 at Buls Maytag, Rockville (231-0844), Silver Spring (589-3363), Vienna (281-4890), Springfield (644-2977), Alexandria (765-2206).

Maytag washing machine, model A512, 3 cycles -- $468 at J.R. Enright, Chevy Chase (654-1700). TYPEWRITERS

Royal Alpha 2001 typewriter, daisy wheel, automatic correcting feature -- $209 at Evans, Rockville (770-6400), Arlington (892-2800), Alexandria (256-6700), Fairfax (425-9000), Manassas (631-2333).

Olympia Compac II typewriter, daisy wheel, automatic correcting feature -- $345 at Office World, Herndon (471-9555). Silver Reed EX-42 typewriter, daisy wheel, automatic correcting feature -- $339 at North's Office Machine in the District (466-2000). QUEEN SIZE MATRESSES

Sealy Imperial queen-size mattress, matching box spring -- $289 at Custom Bedding Co., Cottage City (699-1330).

Simmons Monarch queen mattress, matching box spring -- $490 at Denis Sleep Shop, Langley Park (434-0334).

Serta Tranquility queen mattress, matching box spring -- $349 at The Bedstead, Springfield (569-0553).