If you have the air to run a siphon gun they are ok.. but the cabinet must be designed for it to work.. and oh yeah, LOTS of air. Bags of sand from a hardware store can have moisture.. you need 100% dry sand. For play sand you may need to pre-screen it if you see pebbles or make sure you buy screeened sand.. its a little more expensive.
Best bang for the buck is to go to a landscape business (or that sells paver bricks) and get a ton of sand.. will cost like $15 vs $3 for 50lbs at a store. Must still be dry and screened.
If you don't see a lot of blasting in your future then you may get by with a siphon gun... but for large parts (cab, frame) no. Job out the work or get a pressure pot. I actually did a frame with a pressure washer and siphon setup and it worked really well... but a the pressure washer can provide a lot more suction than an underrated air compressor.
