You do not have to buy gems. Try both options under the "FREE GEMS" button that is in-game and of course use tapjoy.com to get a okay amount of gems, well at least enough for the 2 skill points option.
If you're on android your glu credits will be common between other glu games. Load up Dearhunter Reloaded and get 20 every five days for just starting the app. Other games can earn easier than HOD as well.
Comments
Playing eternity warrior also gives you a lot of gems
http://ggnbb.glu.com/showthread.php?50679-Item-Guide&p=85562#post85562
Runic Item Guide here:
http://ggnbb.glu.com/showthread.php?47298-Guide-to-new-Runic-items
DPH, Hero & Party level Guide
http://ggnbb.glu.com/showthread.php?53269-DPS-Hero-amp-Party-level-Guide
Runic item capabilities List ( By rewand )
https://docs.google.com/spreadsheet/ccc?key=0Aon0kRu72Uj7dEtVUWVRQ0Nsd2FteUJqYUlrVkN1V0E&usp=sharing