http://www.pistonheads.com/sales/2086989.htm

is what I'd recommend. Your budget isn't enough for an E46 M3, you don't need diesels. Any "normal" spec 8k BMW will be at an age (and also common enough) to be heavy on depreciation. LS1 economy on the motorway is excellent for what it is, and the seats are uber-comfortable.

Just to be a bit different from the norm. Plus to recommend anything else I'd either be saying add another 50% to your budget or spend half just over half of it. That fits nicely into the middle and can't see them depreciating into nothing, most of that is done already IMO.