First pass might be a 2560 in a schmartboard adapter.
Add xtal, 22 pf caps, 10K reset pullup, 100nF caps on the power lines.
http://www.schmartboard.com/index.asp?page=products_qfp&id=70
I think this is the one - I have a couple, waiting to get some time to try this.
Bootload with AVR ISP MKii like a mega, can expand from there.