The ‘11-‘13 M56 is another sleeper deal. Not near as many out there but more luxury features (cooled seats, adaptive cruise, etc) on the same basic platform but with a 420hp V8 that is also very reliable. I picked mine up for $15k earlier this year.

Just over budget, but reasonable to think you could get it for $4k. You wont tell your kids about a Corolla or a Crown Vic 20 years from now. 7500 RPM shifts in a reliable daily driver though, that you will remember... (and wish you never sold)

If you are looking at used I would skip the euros and go for a G37 sedan. Well equipped (at least no cloth seats). Every bit as engaging to drive as the Euros (and much faster for the price). Far more reliable and 6 spd w/ RWD. Find them all day for $20-25k.