The key, if you can, is to choose a NEMA standard motor, there are tons of suppliers you can get a nema gearbox from. They get pretty small, but if it's amaller than the smallest nema size I'd go to a place like stock drive components which stocks thousands of gears.
The challenge is that gear tooth geometry is often more than 2d, so laser cutting may not be the best solution for longevity. For a quick and dirty prototype it's certainly fine.
standalone gear boxes also seem to be really really expensive
what i would really love is a set of compatible gears that work from the same shank and would allow easy construction of 1:2 or 1:4 or 1:8 and i could compose. maybe some 1:1 bevels too
The challenge is that gear tooth geometry is often more than 2d, so laser cutting may not be the best solution for longevity. For a quick and dirty prototype it's certainly fine.