It will be possible to run from a generator, however it will need to be sized appropriately.
Best option will be to phone a couple different generator suppliers, explain to them what you're powering, and see what they suggest.

My guess would be aim for a generator with at least twice the KVA rating of what you need in total. The big issue will be voltage dipping/surging while motors spin up/down. The main spindle shouldn't be too bad, as the VFD will ramp up to speed off load, so there's no major start-up surge. However the vacuum motors will most likely be a simple contactor control, which will most likely cause a pretty large start-up surge.

And by the time you pay for a suitable genny, that 3k to get proper 3phase will most likely appear reasonable!