My suggestion is to work to your strength You have what looks to be a very rare '71 in that it is not only undisturbed but in fantastic shape except for the body. The interior is A-1 and the exterior trim is all there and in great shape from what I can tell. This alone is worth a lot. Inside looks new and most of all, correct which means you have the potential there for a high-quality restoration.
But these cars have no frames and being unibody with blind voids which have no way to drain moisture & tend to rust out from the inside. Please get this car on a lift and send pix.
You can purchase fenders, 'frame rails', floors, doors, subframes and nearly anything you need individually but this gets expensive because it each part gets removed, refitted and welded in or hung.
With what you have I would look around for 'rollers' - there are a few on the board now, from California or elsewhere - that are "rust free" or with minor rust issues. You would be looking for pre-74 "roundies" such as what you have.
I and Mac (and others) are both in the midst of a resto on a '72 which needs far less than yours and will cost about you would pay for a 3-4 year old 3-series (sure he will agree) but we are both aiming for our cars to look original so theres additional burdens.
Just to leave you on an optimistic note, overall these are relatively simple and very durable cars. Don't be worried about lifting your carpet, or anything else. Most anything can be fixed.
Good luck!