My $0.02 on this, in several parts. Note that I've done 29 rolls of C-41 and 5 rolls of E-6, so I'm not yet an expert on this.

First, as Nick mentioned, it's possible to mix your own from bulk chemicals. Various formulas are available on the Web, but I'm sure most of them would make PE shudder. I've used NCF-41 with decent results, but it's clearly a bizarre developer and it might well not satisfy the pickier folks. (I'm sure it's among those that would cause PE to shudder.) FWIW, 16 of my 29 rolls were done using NCF-41.

As to commercial C-41 developers, so far I've only tried Paterson Photocolor chemistry (for 13 rolls), which has the advantage that B&H will ship it. The developer worked well, but started producing very thin results by the time I got about halfway through the bottle, so I ditched the rest. It ships as a concentrate that's diluted for use and can be re-used a couple of times.

For bleaches, fixers, and blixes, the conventional wisdom is that blixes don't do as good a job as separate bleach and fix steps. So far I've only used blixes: I've used a homemade recipe that I didn't like and I've used the Paterson blix, which works better but still seems to produce slightly grainier results than I see in commercially-processed rolls. I'm planning to buy Kodak bleach and fix next. Note that Adorama will ship these (and most other color chemicals), although B&H won't ship the bleach or some other Kodak color chemicals, and Freestyle doesn't seem to carry the Kodak chemistry at all.

For E-6, so far I've only used the Paterson Chrome-6 kit, which comes as six bottles that are mixed into four components (1st developer, color/2nd developer, blix, and stabilizer). The instructions say each component can be re-used up to three times for 35mm. I've gotten good results from the first roll, but the two second rolls I've done have been dark. The one third roll I've done had some ugly color shifts. I'm not sure if the re-use per se is the problem or the storage for a few days after mixing before doing the subsequent rolls. I notice that Adorama lists a Kodak E-6 kit that's specified for one-shot use, so I may give that a try.