35mm Camera Question

Hey, my uncle was going to give me one of his old but new cameras that he doesn't use because he has much better equipment as he is a wedding photographer. He is giving me a 35mm Pentax ZX-M camera body, it needs zoom lens. Now here is my question... say I was sitting in like the 10th row of a stadium, and I want to zoom into the pitcher or the shortstop, what kind of zoom would that require? My uncle said that if I went with a 100mm-300mm zoom lens, I'd be in very good shape. Should I be looking for even a higher zoom? Perhaps 500mm-1000mm? I don't want to spend that much money on this because it is film and definitely there are more pros using a digital these days. My uncle said he'd do free enlargements, 8x10s, 16x20s, I just have to provide him with the negative, he has his own photo lab in his basement. I saw on ebay a couple of lens that go up to 300mm for around $100 or less. Is that sufficient enough to get a real good closeup from like 1-10 rows up? Please help, Thanks.