The rust that you show on your pics was similar to mine, so I obtained a repair panel. I suspect the inner closing panel will be effected, which has to be manufactured by the garage as they are not available. To help cut down the labour cost I removed the rear exhaust box, the rear bumper and the boot carpets. Removing some of these parts gave me the opportunity to treat rust especially on the bumper beam and under the chrome. The garage work cost me £600 which was cheap compared to other quotes I received. The unusual thing was the near side panel was not effected. When the job was completed I sealed around the bumper anchor areas and any entry points to this area with dum dump. I bought some good quality carpet and used the old pieces as a template and was quite pleased with the final appearance. I too had to sell my other car (LandroverDefender) to fund this work. I do miss my Landrover as it was my winter vehicle as my wife uses our Honda CRV most of the time. I try to keep my classic car enthusiasm in check as I have spent loads on previous projects. I think the average person that rebuild cars do not make a profit on them unless you keep them for years, even then it is then down to the type of car and the present financial climate. Anyway I do it for the pleasure of improving a vehicle that could potentially get scrapped back to a good condition.
Good luck with yours