If it's cheap to get done in your area, there's no problem having it welded and re-machined. I've done it in the past and never had any issues w/ it.
Like said before...there are a whole lot of race engines running welded cranks.

If you buy a new crank, at the very least you'll have to have it balanced. Definitely not a drop it in and go type of deal. Depending on what crank you buy, it may or may not need some corrective machining to be useable. Not uncommon for the cheaper cranks to have to be turned .010"/.010" to make them useable after you buy them new.

As to why yours ate the thrust...could be a few things. Converter ballooned, not enough clearance b/t converter and flexplate to start with, thrust not "set" when built, an out of balance issue, etc.