New unit or repair?

I am a homeowner and have a 10 year old Trane 2TGB3F30A10000AA heat pump at a townhouse in DC metro area. The A/C didn't come on when I went to use it for the first time this year. I called a local HVAC tech. Initially he thought it was a leak in the sytem, but later diagnosed it as a faulty TXV. He ordered a replacement which ran about $350. As part of replacing the TXV he said he would have to completely drain the R22 (and not reuse it) and then refill the system with 8 lbs of R22 ($100/pound -- called around price/lb is correct). I find it strange you can't reuse the R22. Is that correct?

He tried to screw the new TXV on (the coil?) and it wouldn't go. He called Trane support and explained what he was seeing and they had no answer as to why it didn't fit. He verified the model numbers were correct. Does that seem possible?

Since the TXV now won't fit he priced out a whole new coil from Trane. Trane wants $800 for the coil. Add in the labor, the new R22, and it seems like I'm getting to the point of replacing the whole system.

Is it possible to just replace the inside air handler portion of the system?

Thoughts? Advice? This is a rental property. If I need to replace the entire thing, I don't need a top of the line system. I just need something that is reasonably priced that will last 5-8 years until I sell the house.

Thanks!