Part of the problem is he's not going to know what it needds until he gets into it - if it needs a new R&P, it's going to add at least $1,000 same with gears with chipped teeth, etc. If you get a quote - expect a low/high range of $3,000 to account for broken / damaged parts inside
Unfortunately, transaxles are one of those things you can't really give a solid quote on until it's open.
That said, JW is a solid guy and would be on my short list to rebuild my 911 transaxle.
Regards,
Andrew M