The process is automated (much like the roller-transport processors that used to be widely available for colour print processing in a home darkroom) and for the sake of chemical conservation, a lab usually has at least two processors (one for C-41 and another for E-6) -- load the film and push a button. Most current pro processors are multi-format (110/135 or 135/120/220). Push and pull processing usually require separate batch runs.
Are they fail-safe? Not really (that would be almost impossible, and certainly impractical, since it would mean yanking partially-processed film out of the soup, stopping whatever chemical process was going on, then later restarting at exactly the same point in the process) but processors are usually calibrated daily, have chemical-life monitoring and closely-regulated temperature controls. Because they use large amounts of chemicals, and chemicals are lifetime-limited after mixing (as well as being exhaustible by processing) they're not the sort of thing you'd want to use in a low-volume operation. There used to be intermediate-use processors (machines that used about a litre of each chemistry type) from companies like Durst that would be suitable for an individual pro's in-studio lab, but most of the companies that made those processors have either gone out of business or turned to other products since digital photography became the big player in small-format photography.
As for price, well, somewhere between a low-end luxury car and a nice house is the kind of range you're talking about. For C-41, a full-blown minilab can be cheaper than a soup-only machine, just because they're easier to find (a lot of small operators have left the business behind in the past couple of years).
All that being said, unless you are planning to take in lab work from other photographers, then looking for a used intermediate processor -- one that uses essentially the same coil-in-cylinder system that you'd use for hand-processing, but does automated chemistry swaps and agitation -- is a much saner choice. New, they were in the $1-4K range ten years ago, but you ought to be able to find them considerably cheaper these days (the exception being that 4x5 and 8x10 accessories are still going to be in relatively high demand).
