Some of the paint primers available at the Auto Zone or Home Depot will give you reasonable results. You can do a lot of research on the internet to figure out which ones are acceptable. If you get into the habit of buying whichever spray primers, sooner or later you're going to get a brand that has larger flakes that expand upon drying, ruining your primer job, wasting your time, and forcing you to strip and start over.
I'm incredibly picky about the primers I purchase. (I'm also the only person at Battlegrounds I know of who primes white!) There's a real difference in performance even between such brands as GW and Armoury, but if you're not getting too obsessive then you don't have to be so uptight.
