Maybe a bit Rube Goldberg, but likely quieter than any stepper...
Take virtually any small DC motor and gear it way down using pulleys that fit O-rings, or timing belts if that works better. Have one or more indexing pulses on your disc or whatever that are connected to a simple microcontroller (these have now become ubiquitously referred to as "Arduino" noweadays, regardless of what silicon is behind the system). Use very simple PID to control the motor RPM. There may be some discrete circuit that would work, but with high powered silicon being virtually throw-away there's not much point to look elsewhere.
he RPM pickup could be as simple as a light-interrupting laser-printed encoder wheel or something you've drilled equally on a rotary table setup. Sounds complicated, I know, but the cost would likely be less than the stuff you've been looking at. I guess it depends how tightly controlled you need the RPMs as well. Maybe it would be sufficient to just run it at a fixed voltage you've determined makes the output the speed you want.