I agree, any cheap grey primer would be ok, I also use the grey primer on the wood products that I build.
Ditto what Modelmaker said. Especially about the cleaning. I use Dawn dish soap for that. Make sure you give the primer a couple/few days to dry.
The short answer is: any spray can primer. I usually use whatever is cheapest at Walmart. For brick buildings I use red oxide, which also can work for the brick color, for just about anything else I use grey.
Be sure to give the parts/model a good wash with some grease cutting dish detergent to get rid of the mold release and finger prints.
Jay
C-415 Build: https://imageshack.com/a/tShC/1
Other builds: https://imageshack.com/my/albums
I'm building a kit made out of polyurethane. The directions say I can use any kind of paint, but I "should use an appropriate primer first".
So what's an appropriate primer? Explicit use of brand names is encouraged.