1.) Try to find as better as possible Collet Chuck extension - as cheaper as possible.
Every type could be OK, every shank diameter could be OK - Shank diameter ---> Bearings. If you have access to good Shaft-Grinder - you can resize some used collet chuck to needed diameter (ID of bearings you found. But this Shaft-Grinder must to be very experienced/practiced/versed !!! Unfortunately very often they are not.
2.) Try to find as better angular contact Bearings as possible - as cheaper as possible.
To engrave medals you dont need 1...2 kW motors I used. Even for my works Im doing my last motor is too powerful, but it does not matter for me. I hope I can tell you about near every motor you have found - is it OK or not - you have only to ask about.
Summary: you can keep your budget much more lower level.
I do not sell my spindles! I just gave some ideas for people who like to try.
I have Kavo 4025, I have Elte 350w, I have few more HF spindles I have bought from eBay for study how they are made - I dont use these asynchronous spindles - I like my DIY BLDC spindle.
Regards,
Herbert