To test my theory that you can get good results from any primer, I picked up a can of the ColorPlace (Walmart brand) Primer last night. The advantage of this stuff is the fairly universal availability in the US and rock-bottom price. After tax, the 10 oz can cost me $1.12. Make sure you get Primer, not paint. Check the back of the can until you find one with "Primer" on the label since at my store all of the grey paint and primer were mixed together on the shelf.
The label says to spray at 12"-16" away but from my own experience that is just way too far when using short, quick strokes. I sprayed at about 6" on a pretty windy and humid morning and the results were good. ColorPlace primer was not as smooth as some of the more expensive primers, but this was only my first attempt. I am sure better results can be had with some more experimentation and better weather conditions but I am satisfied with the results already. The grey shade is about the same grey as Tamiya Fine Surface primer, which is a lighter grey than GW plastic.
The can also says to spray a second coat within 4 hours, so I'd let is dry at least that long before painting but the models were dry to the touch within 10 minutes.
There was a large selection of spray paint at my local Walmart but they were out of the white ColorPlace primer. I talked breifly to the "paint guy" working the area and he said they now only make grey and white primer; no black. Your mileage may vary at your local Walmart, but I know that a lot of people really won't use anything but black primer.
Here's a quick video of the technique I used.
Got a can of primer you haven't had any luck with? Lemme know and I'll try to find a way to make it work.