k100 is a good starter for around $30 but you will need a battery and charger if you dont have one already. A good dual coil that is easy to build on is the Phoenix V10 and it is about $20 from Altsmoke. It has adjustable air holes. For what it is worth they all have adjustable air holes... i drill them out till i like them.
If your planning on going sub-ohm make sure to read and research all the Ohm's law and battery safety stuff. Its important to know what amps your drawing and your batteries C rating. Have fun and be safe.