Good paint is very pricey. I would shy away from acylic enamal (AE) as that is yesterdays technology. AE paints would be around $200/gal.
For a little more $, you can get acrylic urethane (AU), which is a single stage paint that offers alot of the benefits of BC/CC systems without adding that shiny plastic look to your old truck. AU paints are around $300-$500/gal.
If you want that shiny plastic look, BC/CC is the only way to go. Here is where pricing gets tricky. BC/CC systems can be cheaper because they are more forgiving. They are easier to apply/buff/colorsand, so it may be significantly cheaper than AU for a shop to apply and deliver to you.
Do you know the exact brand, model, type of paint that is being offered for $350/gallon?