There are some decent metal etch primers sold in spray cans. I use SEM brand.
For primer to block sand or to cover filler, you really do need something with a catalyst. Spraying at $23 a serving for what you have been using will add up pretty fast. A gallon of Evercoat high build "Slick sand" will cost you under $100 and easily cover the car twice. You do need an air compressor and a spray gun though. I have had decent luck using the gravity feed paint guns from Harbor Freight. They can be bought on sale for less than $20. The compressor is the most expensive part of all of this.
Once you get an air compressor, you might find that you like using other air tools. I like my air ratchet, impact gun and air chisel. The blow gun also is fun to annoy the dog.