There is a few items that I often buy and sell, such as steel Equipto
desks. They usually cost next to nothing on auctions and easily sell
for $100.

What I want to do is to set up a sandblasting and painting operation,
where an $11/hour guy would sandblast them and then paint with a spray
gun. Maybe he will spend an half hour per desk, sandblasting and spray
painting, and I can charge extra $50-100 for a "freshly sandblasted
and painted" desk looking like a million bucks.

We could sandblast in our backyard and paint right there.

We have a 10 HP reciprocating compressor.

My question is what options do I have regarding blast media and blast
guns. I heard about silica sand being harmful for health, and wanted
to know what are the reasonable low cost choices that are safe to use.

Thanks

i