I found my Diana in a church attic sale, complete in box with instructions/unused strap and paid something like 25¢ or 1$ for it.
I recommend you hit every yard and attic sale you can find until you score. It might be awhile before you find what you're after, but I'll wager you'll score unlooked for photographic treasures for all your 'trouble.'
Besides, jumble sales are tons of fun, bargaining down the prices, the thrill of the find and they are ripe with opportunities for good shots, so tote a camera.
One last thing, always ask if they have any camera kit they'd be interested in selling and tell them your are ALSO interested in toy cameras. I can't tell you how many times people have brought out stuff they forgot they had put up somewhere, most of the time polaroids, but nice stuff as well.
I've picked up two SLR outfits, with cases, bags, extra lenses, etc like this and paid a pittance in the process. Always ask what they want for stuff first, often times the price will be so low you won't feel the need to haggle and since they set the price they wanted, there's no reason to feel bad about the really great deal you just got.
Cheers