Rebuild at Mackies or better at ZF in Germany (this is where I go).
Yes, that will cost a lot of money.
But it won't be more expensive than the money
.
Get rid of the car now if you are not prepared for full rebuild.
If you're lucky, you can find donor gearbox, but that's lottery.
Rebuilt will always be cheaper if you do it immediately after you notice first symptoms. When done, change ATF and filter every year if it's daily driver. That's what I do.