First developer can be very cheap, even if you don't/can't replenish it (I've seen pictures of what looked like good results with Rodinal 1:25, 15 minutes at 40 C, though it was full strip images, not frame scans). Color developer is the one that costs, and I've done C-41 (Flexicolor LORR) replenishment at only 2-3 rolls a month with good results through a liter of replenisher (most of a year). Bleach and fixer you just reuse to capacity (even C-41 chemicals will work here). Question is whether you can get a replenished system color developer for E-6, more than whether it's practical to do. Mixing your own is one way; there are published formulae, but I understand some of the chemicals are hard to source or have impractically large minimum orders.
Kits are an option, and still cost a lot less than sending your film out, but what I'm planning to try is getting just the color developer (I ordered from Cinestill, in transit, around $1.50 per roll at their listed capacity), use Parodinal for first dev and Flexicolor C-41 bleach, fixer, and final rinse (I'll order in some formalin if it seems I need it for stabilizer; my darkroom is well ventilated). If this works well with expired 35 mm and 120 films I have, I'll try it on the fresh box of 4x5 E100 I just got, and it that works well too, I'll try to get either a short end, recan, or next year's tax refund will go for a 400' roll of Ektachrome.
