My top three suggestions would be an RN4081, a Joye510, or the Ego.
Sadly, the RN4081 is getting hard to come by, but that with a cartomizer and refilling has been my hands down favorite. Azsmokefree has some pretty affordable kits for both the RN4081 and the 510. Their deal on the Ego is also hard to beat, when they have them in stock, at around 50 dollars each for a kit. My only drawback to this company is I do not like their juices and the prefilled cartos can be a bit "bleh". The upside is the prices are great, and shipping is super quick.
Another low price option is ValueVapor. For 510 stuff they are really good and the prices are very very low. Shipping here is also pretty darn fast.
Neither of these companies are listed on the vendor sites here, not sure why that is. I've had no trouble personally with them, except of course, I avoid the juices.
Be careful buying juices though from low price sites...... everyone I've tried has been pretty miserable. User results may vary.