Having established that it's a ****, finish wise, I'd have someone you know take a look at it in order to verify it's mechanical condition and check the timing.
If it functions well, then you "could" buy it and just shoot the hell out of it and get your money's worth in fun because you'd never have to worry about collectability due to it's condition.
Or...
It's tempting to buy a "cheap" pistol like that, and another way to look at it would be that if you had it Metaloy'd and put a new set of wood grips on it, you'd have a total of $600 into a "brand new" pistol that could be your shooter for a lifetime and not ever worry about the finish again, nor worrying about ever wearing it out (it's a 28 after all). In this case, you'd be proud of it because it would always look like a new pistol, but you still wouldn't have to be concerned about collectability.
In that case, you'd have more into it than you would had you waited for a very nice original example of a 28 that would retain collectability, but the nasty looking finish of the original wouldn't weigh on your brain all the time.
I don't want to suggest what to do. I'm just showing some options that might help to better decide if $270 is really a good price for this pistol.