In general low level masters are either extremely rare, or extremely overpriced for new players.
Your best bet is to just not worry about masters too much until you start coming across the "irreplacable" masters (Dark Heart at 18, raidwide Heart at 73, Dooming Darkness at 51, Resurrection at 48, and everything level 81+, I believe). Anything that's not irreplacable gets upgraded. And for the irreplacables, the Research Assistant is your friend.