I'd go with a mid priced variable voltage/variable wattage set for the next step, along with a Kayfun style, single bottom coil RBA. Teh MVP 2 and the Ehpro Kayfun Lite will run you about $70 - $80. This way, you can learn about resistance, voltage, wattage, amps and how it all works together before you jump into a mech mod. If rebuilding doesn't suit you, you're only out about $30 for the Kayfun clone and the MVP will work with almost any clearo on the market. If you don't want a box mod like the MVP 2, look for a regulated tube shaped device like the SVD, Provari or Semovar. The MVP 2 does make rebuilding easy though. You can check the ohms before firing, unlike the Provari which fires the topper in order to check ohms. While the base is still attached to the MVP and the ohms check out, you can then fire it to set the coils and oxidize the kanthal, eliminating the need for an ohm meter.
If you do want to skip the regulated, APV step, I suggest that you get a Kick. The Nemesis is a great mech mod that'll take the Kick in any mode. The Kick will offer you some protection against shorts as you learn, as well as keep you from over draining your batteries. The Kamry series of mech mods are decent, genuine mods that aren't that expensive, as well as the Smok Magneto.