[Lusticles]

You can find any E46 (minus M3) for under 20k.

A lot of E90s too.
You can get a fully loaded ZHP with decent miles for under 20k.

 

[Lusticles]

You can easily pick up an M3 for under 20k:

http://www.m3forum.net/m3forum/showthread.php?t=309081

No M3 sedans,tho.

Yes you can. Though it would have been improper for me to say any E46 including the M3, since a lot of M3s cost more than $20k.