A siphon system is the cheapest type of sandblaster setup. In fact, you can even make one yourself quite easily. A pressure pot can be made also, but it is a little more complex than the siphon blaster.
Since the siphon type is very cheap, I would recommend that you buy one that is already manufactured. They can sometimes only cost a few dollars, so might as well purchase one. The cheapest ones will consist of just a hose that you stick in a bag of abrasives and a nozzle gun. The nozzle gun is connected to the abrasive hose and the air line from an air compressor. Once the operator pulls the trigger of the nozzle gun, the compressed air flows through while sucking out or siphoning the abrasive from the bag. The abrasive then gets mixed into the flowing air.
Since the compressed air has to work on two different jobs at the same time, the siphon setup requires a larger air compressor. This larger air compressor is needed to power enough air for both duties. The duties are to siphon the abrasive media from a container and then blast that same media out the nozzle. Which is then aimed at the surface to be blasted.