Don't let the naysayers discourage you, there are lots of two seaters out there for $20k.
There was a Model 1 Kitfox in flying condition sold for around $10k on ebay a while ago.
Older kitfoxes or avids are out there, don't have all the fancy of newer $100k machines but very good performers.
If you are not stuck on side by side you can often find Chinooks or Challengers for that price, they are good solid performers and have been around for a long time.
If you keep an ear down there will be some Sonex's out soon judging by the number being built.
What you are looking for is going to take a little work to keep flying though, these airplanes are a bit more "fragile" than your spamcan Cessna's and Cherokee's, but the performance is FAR superior.
These new $100k LSA machines are for the guy who is afraid of going to the doctor and knows he has to give up his Bonanza.
Us ordinary working guys can fly and it doesn't need to cost more than a Harley or Polaris.