on another note:
...you may wish to do a search on this...I faintly recall a post saying the the 400e/e420's were made in Mexico - hush.hush? (or something of that sort)

you'd probably get the most out of your $20k by purchasing as new/low mileage and well-kept/maintained a vehicle as possible no matter what the candidate (although that pretty much rules out garage-queen 500e/e500's ie autotrader.com has a couple of '94 e500's close to $50k asking prices which means over $50k with taxes & reg fees / and a couple of 20K mile odo '92-'93' 500e's in the $30k's)

as other choices:
>seems pricing on the newer e-class sedans are dropping to your stated range too
>I've also seen a few low mile 560SEC's or 560SL's in that $20k's range

hope this helps