I'm glad to help, it's part of how to keep the hobby alive.
I use a few different primers depending on what I'm doing.
The economical gray and white Krylon primers work well for checking body work (and prepping die-cast pieces).
Tamiya Fine white and light gray primers are excellent, but a bit pricier and work very well just before putting and color down.
I also used catalyzed two part automotive primers for some of the larger subjects. PCL High Fill Poly-Primer is a good value.
I buy from my local paint supplier. Since I worked in the auto painting industry I just keep going back to the same store. I've found most shops are fine with "non-professionals" and hobbists buying direct.
Last time I bought The Matrix I think it was around $50-$60 for a quart of clear and 8 oz of activator. Stored properly it will last quite a while and you can paint a lot of bodies. Valspar also makes a good clear as does PCL which is usually more economical.