...also, where can one find the RS232 filters, other than Patrick? Mouser and Digikey seem to be of no help. I was able to find them on Newark.com, so I suppose I can order from them if necessary. Seems a minimum order of 5 at ~$4 each plus a $20 handling fee does not make them cheap.

Other than the RS232 filters, my totals for all of the bits for (2) boards at Digikey and Mouser, were $129.20 and $83.53, respectively. So if you do it yourself, you can pretty much have two sets extenders for just slightly over $300. Not bad, considering.