Julian, I use C41, or to be more precise, a variation, I use a mixture of proprietary chemicals and my own darkroom mixed chemicals.
The best bet for you is to work out what your country sells to the trade and see if you can work around their 5, 10 or 20 litre kits. Mostly you'll find, from 5 litre upwards, the cost really starts to plummet.
The same goes for the paper printing side of the system. I use RA4 in 5 litre kits but as they were/are Agfa I'll be looking at Kodak or Fuji kits designed for mini labs. I raised the question recently and the replies basically said that the 20 litre (or 40 cannot remember) kits were in lots of ten litre mixes with the bottles labelled so that one can mix up different amounts. I myself need 2½ litres for my paper processor so I only mix up that amount.
For C41 I would suggest that you look at what's available locally, get the minimum amount, run a roll or two through in your Patterson tanks and see how you go. I think you'll be pleasantly surprised at just how easy it really is.
What country are you in?