If you are looking to get in under the $500 dollar mark and really learn 3D I think you may want to look at a profile. I have never been a fan of profiles until I finally broke down and got one. I got the Extreme Flight Chinn Yak 55. It is now my favorite plane for sport 3D bashing. I have learned more about 3D with this plane that any of my other planes. THe U-Can-Do is a fun plane to fly but it is NOT a real 3D plane. I would look into purchasing a profile for a first 3D plane. Here is a couple suggestions.

Mojo 40 ARF
http://www.swanyshouse.com/mojoARF/mojoARF.aspx
Best 3D trainer on the market, hands down. Probably the one I should have bought. PLus their is an exact replica of this plane that can be downloaded to RealFLight G4 for practice. Shoot me a Private message if you want the file.

Chinn Yak 55
http://www.extremeflightrc.com/html/ChinnYak55SP.html
This is the higher end of the 3D profile performance envelope. It is an amzing little plane and can be outfitted with quality gear for less than $500. I have met the designer of this plane and it pretty amzing what this plane is capable of.

I strongly reccomend trying out a profile to learn 3D they are cheap, fun and they will get you the skills you need to move on to bigger stuff.