Given the high market value of your Merc and the high cost of good used parts, fix it. If it were a lesser valuable car I'd say look for some cheap replacement parts. Your car is probably worth more repaired that the cost of the repair. Thats pretty much the economics behind any spending justification. Of course not everyone is subject to the same spending rules for any number of reasons.
It can be done, a local did 100 hours of "smoothing" on one of his mercs and got it looking something like this. He is good, but he aint a bodyman either... trim fit, trim fit, trim fit tack.. next piece s.
A Welder, Grinder, And A Good Flap Wheel Can Fix Anything, Even A Broken Heart, Probably Not A Broken Neck Though So Make Sure That Rust Didnt Get Through The Frame.