If you're looking for cheap sand - check out blasting sand at a local masonry supply. It comes in different sizes so you have a choice how fine you'd like. Around here, it's only a few bucks for 100 lbs. I purchased sizes 00, 0, & 1 several years ago.
However (probably like the grit), you'll want to test it for carbonate-type stones (that will increase TDS and pH). Our local stuff is almost completely inert quartz-type stone & works great once it's rinsed well. However, when talking w/ a friend in Los Angeles, he said all of their blasting sand was unusable. Since the stuff is heavy, firms will source local material whenever possible to reduce transportation costs - so YMMV.