Yeah, I mean, I could do the repairs and they would be pretty straight forward, but the sheer amount of time required would make it something I would rather not attempt. Plus, if it is that bad in that section, it is likely there is other damage waiting to rear it's ugly head elsewhere on the door. Also, most body shops will do the minimum possible to get it out the door ( if you believe in paying for this sort of thing) and likely will not treat the back side of the repair. If you wanted to do it yourself, you could take a piece of sheetmetal and bend it over a straight 90 degree cut piece of wood like an old counter top, cut out the rusted metal, butt weld in the outer portion using a series of tack welds ( NEVER a full bead on sheetmetal! it will warp due to excess heat!) allowing it to cool between rounds and then use a pair of flanging plyers or a hammer and dolly to bend the lip around the bottom. This assumes the inner structure is still there to bend it around. If it no longer exists, you will have to make a new piece of metal to repair the inner structure first before patching it. On the plus side, it is a flat section of metal behind a trim piece so you can hide it with the trim if the repair is not the best quality. There is also the less than ideal way of joining the metal together too, and that would be a lap joint using panel bond instead of welding to join the two pieces of metal.