go for the expensive models, as the hundred dollar ones dont work so well
I'd qualify that statement a little. $50 butane powered vapes like the VapoGenie and Vaporstar work well with the proper technique, and for $120 you can get a very good, very reliable, standard Vaporcannon with a 5 yr warranty. The cheaper, no-name, or off brand whip models would worry me. Most of the bargain box vapes you can get on ebay have no warranty.