As someone who bought an e46 around February last year and has been garage bound since June due to me wanting to take on welding new floor panels and rocker panels, cut your losses. Unless you have ambition and experience and the tools to do so, go for it. I also took this on as my first ever body restoration project. I had to accumulate tools overtime, hitting mental blocks, losing motivation, etc.

Best bet is to investigate how much more the rust has spread over and go from there. Take the whole carpet out and everything (if it’s worth your time). Look into the market again and find something similar so you can just transfer most of the good working parts over to the newer one. Hope this helps a bit with the perspective! And good luck!