Use this tool... it is comprehensive and very accurate (assuming your numbers are)...
http://www.leaseguide.com/calc.htm
A .0005 money factor is roughly 1.2% interest rate. That is very, very low. Do you have that in writing?
If I input your numbers into the calculator, before taxes, assuming $0 money down and $500 extra in fees (aquisition fee, dealer fees, etc) you are looking at just about $500/mo before taxes. Are you putting anything down or trading anything in? If the answer is no then their quote is a great one. I would have that in writing or if they honor it don't try to find out why.