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Macodirect sold C200 for 4€ per 2-pack. That's the cheapest film of all, including bulk reels of Fomapan (2,50€-ish/roll). And it comes with a cartridge as well.
Caveat is of course that it's only cheaper than black-and-white in HC-110 if you use a 5-liter C41 kit to its full yield of 100 films (or something even cheaper, such as using the baths past recommendation), which means 200€ just for the film alone, and 34 sessions of heating up the liquids and so forth. Developing in a lab is obviously quite a bit more expensive still.
If you develop at a lab, film cost is a false economy. You should shoot less and better; this yields more good pictures per buck.
