I think you nailed it, if your on a budget Zap Primer is a good paint. I've sen it for 45-50 a case and I've shot at least a case of it and it was pretty strong. Maybe not the best shell like you said but it held up well for the price.
So outside of the "expensive" paint, I'd say Zap Primer, PMI Premium (kinda inbetween mid range and expensive), and I've also had some sucess with Spank but I only shot one or two bags of it.
I'd go with the Primer if your on a budget. But don't let them sit!! They are pretty greasy and I let some balls sit for a month or two and they got nasty.
But if you own a bushy/FS.. you bought a good gun so give it good paint darnit! Feed it all the evil/blaze/chronic/midnight it wants.