$5,137 is the answer. I'm a CGA and ran it through my amortizaion schedule, here is one from the web that works well also.
http://www.bretwhissel.net/cgi-bin/amortize
This comes up with $5,137.51. $280,000 amortized over five years, monthly payments p+i at 5% with 10k down at the end.