I can only offer this, I bought some really cheap primer from Home Depot (that's what I asked for) for $10 a gallon, and the stuff didn't cover well at all, then when I tried to paint over it, it seemed to **** paint up like a desert. Moral of the story, don't buy cheap paint.
The "good" primer I bought ($25/gallon) went on smooth, covered well, sealed the drywall and the top coat went on smooth too.
In our area, True Value stores have Dutch Boy on sale for half off, that's what I've been using in my garage and boy howdy is it some nice stuff! And at $12.50/gallon, it's a good deal.