Plymouth Gold Duster

I went and looked at it, it starts up nice,interior is "ratty" no carpet, door panels toast, B&M shifter. Nice aluminum radiator. It has a plate welded on the outside LF frame rail,and rust that you can see on the engine side. That is a issue because I don't know whats under.I would want to redo the frame rail where it isn't a plate welded over it. so, I don't want to be into the car much money wise and if I want to sell it be in a predicament with the welded plate in the frame. I offered 3 grand, but the guy said he has offers like that all day. I said put me in line if the others dont work out.. I had the inclination to up the offer to 3500, but after talking to the OL last night she said about "finishing the one you already have" i said "yeah I can throw w the money into the interior of the dart and have change." I dunno, it is a nice "drive home condition Duster, I feel though that I would be committed to fixing that frame rail the right way or id be stuck with taking a loss on the car. Rest of the body seemed solid though. I am on the fence. I would even pay $3500-3800 but like said id be comitted to fixing it,and it would probably sit a while before I do. Another part o fme thinks that at 4 grand , save 4 grand more and there are nice down south rust free cars out there for 8-9 grand...