Steel wool with some oil will do good for the metal, as long as you keep using it, it should keep the rust off for the most part, or a light oil rub of any kind is good.
Anything under $1.00 / lb is good for weight cost, especially if in Olympic size.
Do you have a basement? If you are dropping the weights, check out a local carpet store and look for large scrap pieces and stack them up. You could even tie them together to create a tighter surface that wont fall apart. I wouldn't workout on a wooden porch or floor, but would use a sheet of 3/4 plywood to place above the grass on top of the carpet, that you can easily move when you are done.
Make sure to check there are no stress fractures in the bar, if not, great find!
Good luck and Enjoy.