I don't.... I'm only going to sell them as complete kits. The target price for a 2-channel UCD180 basic kit is $600 complete. It is a little more expensive than I could have designed them for strictly 2-channel use because the transformer, power supply & chassis are all oversized (and more expensive) relativle to what you would normally use for a 2-channel amp.
For the four channel amp you would want to use the five channel PS, 625VA transformer, softstart and four modules. I'd say you are going to be right around $900 depending on which modules you choose and how much capacitance you want to populate.
A UCD400 based version would not cost much more. Just the additional cost the modules.
Build time is only a couple hours. It all bolts together with the only soldering required being on the XLR & RCA inputs. The rest is crimped Faston connectors.