cheap primer for a spray gun

Doing a primer coat on the beater mini truck. Body is as straight and prepped as Im going to get it and I want to give it a final coat of primer so its all the same color and wont rust before we actually get it painted its blue color. I have a spray gun (an older binks style craftsman and a new HF 'purple' gun. I want to use the gun so I can get used to how it sprays instead of just buying a case of $1.99 Walmart spray primer. $21 for 8 oz? That's alot of spray bombs.....No 2K paint just a super cheap first car DIY single stage acrylic spray job in the driveway.
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