There is no question but that mixing Pyrocat-HD from scratch will work out to be a lot less expensive than buying the kit.
Just a word or two on mixing. Mixing of Pyrocat-HD from scratch is pretty routine but there are two areas where some extra instructions might come in hand.
First, phenidone is rather hard to get into solution. A solution to this problem is to first mix the phenidone with a small amount of alcohol (90% isopropyl best) and then add this to the stock mixture. Be assured that this will have no impact on the working qualities of the developer.
Also, when mixing the potassium carbonate please be sure to add the carbonate to the water very slowly, while mixing. When mixing the carbonate with water an exothermic reaction takes place and if one adds the carbonate too fast to the water the solution will get very hot.
Finally, do allow the stock solutions to stand for an hour or so to allow all of the chemicals to go into solution.