I'm not a 7 expert.... but....
 

How hard would it be to repair a sub frame on a 7? And would it be worth it? There's a local guy selling a flawless 7 but it has some sub frame rot that's in one concentrated area, and I'd love to put it on the road as a drivable second car (so I can give my current 7 a rest), but as it sits it won't pass NYS inspection. Any help would be greatly appreciated.

Edit: I see how narrow my question was. I'm wondering by subframe if he means part of the unibody frame, not the k-frame/k-member. If it's that, I've swapped a few of those out in my day, but if it's part of the unibody frame, would it be worth it? I'm aware I could weld in a piece of c-channel frame from a t ruck or something then just undercoat the car and they'd never know the difference.

The subframes unbolt... I believe subframe on the RX-7 always refer to the front and rear "K" members.

Just grab up some good ones off of a junker.