"so is it common for someone to go and get a low hp three phase electric motor rewound, or it is simply too expensive for us hobbyists"
It is uncommon for hobbyists to have rewound any motor for which there is a reasonably close generic substitute available.
OTOH, certain machines use motors with a unique frame size, and perhaps a unique number of poles, or multiple pole combinations.
Most motor shops are now using a "flat rate" book, often Vaughan's, which gives the average shop time in hours to rewind a motor. This shop time is then multiplied by the shop rate to give the wholesale cost to rewind the motor. The shop's profit and/or retail mark-up is added thereupon.
For example, a 0.75/0.375 HP constant torque 4/8 pole "consequent pole" motor for a Hardinge lathe costs about $440 to rewind from 230 volts to 460 volts, or vice versa.
Repairing a failed motor would cost the same, and a voltage change could be accommodated at that time.
Basically, the "flat rate" book is indexed by the motor's frame size, its lowest rated rpm, its highest rated HP, and possibly its voltage.
Most motor shops are now using "inverter duty" wire and insulation, anyway, so that, at least, is no longer an extra cost.
It is not uncommon for motor shops to be asked to rewind instrumentation motors, including tachometers, and most shops are prepared to do this job as well.