Do you have an estimate about how much time you've got in each? I would charge cost of materials, plus what you consider a fair wage for you. If you ever think you might do it again don't undersell your self (well, really don't ever undersell yourself, but you know what I mean ). I would think about $10 an hour fair...or there are many threads about charging per sq inch, if you do a search you'll get a ton of 'em I'm sure! ;)