You do have another option - generator, or engine-driven
by
If you find a big Syncrowave cheap enough, you can always hunt down a 3-phase 240/480V generator set to run it.
Or start looking at the purpose built engine-driven welders, some of them have output settings suitable for MIG and TIG - you just need to add a wire-feeder and torch to do Flux-Core and add shielding gas to do MIG, or a TIG torch gas and a water cooler to do TIG.
If you end up doing enough welding to where people are paying you, save up your money and you can get that new power line run to your shop later - then the generator is your backup supply.