I checked my inventory, and I have used tested Interfacer-3 (174C) and Interfacer-4 (187C) boards with 90-day warranty in stock for $150, plus shipping. Boards will include cables if I have them. Might also have new boards, but I keep those in a different place, and won't go dig for them, unless you want to pay New List Price (around $350-$400 each).
Also have one Interfacer-3 (174C) and one Interfacer-4 (187C) boards that are waiting for testing. I have enough working/tested boards that I wasn't in a hurry to test these two boards. Will sell these AS-IS, No Warranty for less money with the understanding that what you see is what you get, and you better be able to fix them if they don't work.
I know you didn't mention wanting/looking for a Disk-3 MFM hard drive controller board, but I have a couple available for sale cheaper than normal, because they are early revision boards (194D), and I don't have the PALs to update them to the current level/step. Because the PALs were revised, these Disk-3 194D boards will not read my house system hard drive (formatted with my current revision 194G Disk-3), unless I reformat my hard drive, and I'm not going to do that.
All boards come with original Compupro/Viasyn Hardware Manual.