Also remember if you want to apply special effects it will cost you rep....
For instance if rolling for Lvl5 efficient beams and you get a good roll with no effects....If you want to apply regeneration it will cost you 2 rep and knock you back to Lvl3.......Then you will have to roll your way back to Lvl5......So quite a bit of material can be used if applying effects.
*Edit*
Forgot to mention if you do get an effect with a roll but want to change it, it will cost you 1 rep.