well, what process are you talking about? i can cut freehand maybe 1/8" details in contact paper and that's pretty cheap.
if you're talking about photoetching, you need the special films, you can use the sun for exposure although a UV light is recommended, a high pressure hose for washing out the exposed portions of the film. you then need the compressor and either a pressure pot or a grit recirculating blasting box (for that you need a larger compressor).
you can get halftones with photoresist, which is good enough resolution to get recognizable b/w pictures out of.
you might be able to get started doing this for $750 for everything.
see
you can look over
you can use etching cream through photoresist too, although abrasive is more common. you don't have to worry that the carrier of the cream won't also dissolve your resist. they also have photoresist that you can put on silk, use glass paint, and after firing in a kiln, you can basically do tshirt silkscreening onto glass blanks.
both. when it has to be detailed, there's not an easy way to cut a resist by hand (interior dots, for example), or you're doing more than one, then photoresist is the way to go. for broad kind of blasting, i cut it by hand. for example,
your talk about consistent blasts is also misguided. when you get good with a blaster, you can do broad expanses at a constant depth using a blaster. it just takes practice, and it doesn't come out well until you do get good.
regards, charlie