74 rd350 tires?

Yes I admit. Im a N00B. I want to get some new/"can you use used tires" I
dont want to spend hardly anything. If that helps. Dont flame me but I was
looking at jcwhitney's... Is there another source for cheap tires? I bought
the 74 rd350 for $80 5 years ago. Picture a full sized car battery strapped
to the seat and brown lamp cord to the terminals. I think I just want to
sell it....... What tires fit it. I dont see many 3.00 18" 3.50 18" out
there.......

Thanks for any help
4ndy