Okay hang on but I don't get this. You are thinking of buying a lens, but have no idea if it's going to be of any use?! I thought people bought things because they had a use for it... now I know the truth, want to buy something first, then think of a reason to use it and if you can't, get help from other people...
Remember your initial post mentioned nothing about the cheap 300/4, you even asked which 300 you should buy, suggesting there wasn't a cheap 300/4 initially... so you wanted one why? Aside from it not being necessary...
As to the 300/4. Yes 300 sounds like a good price. But if it needs a clean and repairing, then, well... you should be very very careful. But from the pictures, I'm not sure it does need a clean, but then they weren't the biggest pictures and there must be a reason why you said it needs a clean.
As to your original question, a 300 is really a neither here nor there lens particularly if you shoot with the full 24x36 dimensions. Too short for major long telephoto work, and too long for normal everyday work.