If that's what you want to do, go for it. $8K sound like the right ball park.

I put a remanufactured tranny in mine at about 275K miles, and I will eventually either have the engine rebuilt or buy a remanufactured engine (hopefully not for at least another 100K miles). The difference is that I don't want a E300 (or a CDI), if I did I would have one. I quit worrying about "office issues" a couple of decades ago, it's a waste of time/energy.