I finally found a good source of framing stock, 'framing4yourself.com'. You pick your frame style, enter in the artwork dimensions and they send you pre-cut lengths with divots cut at the corner for pins you simply insert to assemble:
Each painting is mounted on a wood backplate cut from a single sheet of cheap luan underlayment I got at Depot. It's got a nice smooth finish but costs about $5 for a 4 ft x 6ft sheet. Johnny cut the pieces for me on the table saw and I stained them with true black wood finish:
Bought some bulk D-rings and hanging wire from Amazon to finish out.
For about $35 in materials each I was able to frame all of these with very custom sizing. A frame shop would have cost between $100-$150 each.
