Depending on how much you need, I would check your LFS first. Yes, you can get dry sand online. Marine Depot, Bulk Reef Supply, Premium Aquatics to name a few have a selection of dry sand. Some have free shipping, shop around.
I found some 10lb bags of Caribbean fine sand on sale at Petco online super cheap without any limit on how much you could get. I ordered 240lbs of it lol. Even though it was in 10lb bags they just sent me full cases with 4 in each one. I looked for the best deal for months before pulling the trigger on any of my equipment, scaping and livestock. There's always a deal somewhere.