I don't think you can offer half of asking prices, but 20-25% lower seems to be pretty doable in my limited experience.
I really like my Pearson 28-2. It's really a 29' boat (smaller than your target range), but has a lot of space below for that size and sails nicely. Being under 30' makes my moorage a lot cheaper (it saves me about $1000/year compared to a 30-33' boat). If I wanted something a little larger I would also keep an eye out for the similar 31-2 or 33-2. There is a clean looking 28-2 at the upper end of your price range in MI on Yachtworld:
1985 Pearson 28 Sail Boat For Sale - www.yachtworld.com
Other boats that I strongly considered were a C&C 30 (I liked it, but didn't like the lack of a quarterberth), Islander Bahama 30 (liked it, but the one we considered closely needed too much work). I wanted to see Cal 29 and 31 models, but didn't come across any. We looked at maybe a dozen boats priced in the $15-$25k range (including many mentioned here). I didn't see too much from the mid 80s to 90s in your price range, but more opened up between $20 and $25k. However pricing is very regional and Seattle might be more expensive than the Great Lakes.