Magazine parts are awfully hard to come by for the old Marlin pumps.
I think it's Bob's Gun Shop that carries new replacement walnut stocks for the older Marlin pumps. Wisner's should carry some of the innards. both have web-sites- my bookmarks got dumped, so no links. Dogpile will locate 'em.
If it were me, I'd probly try to rescue it, if the bore looks shootable, but I got a soft spot for old rimfire pumps. Try and get more info if ya can- is the bbl round or octagon? Model # can usually be found on the upper tang, just like the old Marlin levers.
The transverse bolt is a little worrisome, depending on where they put it. Hope it ain't too close to the hammer spring....
I'd of course try and lower that price. With the surgery it's had, and going to need, it sure ain't a collector's piece...