If you're modeling well-weathered track, and will be painting it anyway, you might try mortar sand. I've used a lot for scenery base, but had my track ballasted before I found it. It's almost perfectly sized, pre-washed (yes, there is a formal standard for mortar sand) and cheap. I got mine from a masonry supply, probably 20 years ago, and the price then was $20.00 per ton, you haul. I bought about a cardboard box full, maybe 3/4 of a cubic foot. Based on NP hopper loading numbers, and some guestimating, we decided it was about 75 to 80 pounds, so a dollar covered it. They had a scale - for weighing trucks! I still have at least half of it.
For real ballast I used AR&M. simply because they were the only one with colors close to the GN/BN Essex Pit pink rock.