They do grow slowly.
I know this is not what people want to hear, but with slow-growing woody plants (and fruit-bearing ones in particular), unless you stumble on a rare bargain -- and you gotta have enough experience to tell rare bargains apart from common ripoffs, based on the condition of the plant's roots, how it's growing, etc -- you pretty much get what you pay for, at least with shrubs/trees up to about 3-5' tall.
I would suggest that it is much better to pay, say, $15-20 per bush for GOOD QUALITY ones that will transplant well, grow vigorously and bear soon and well, than to get two or three times as many bushes at one-half or one-third the price and have them just sit there sulking for years and years and years. The first way, you may not get as many blueberries (etc) as you might wish but at least you GET them
Blueberries you're best off buying potted plants (not bareroot, which it's too late for this year anyhow). Deciding how much you want to pay for how big a plant theoretically only matters in how soon they begin to bear well. In reality, the different ages are almost never equally well grown. I would suggest buying the healthiest best-grown ones, whatever the age.
JME,
Pat
