So in the temple when you pray you can sell runes for coins.
You can redeem frags fro purple and yellow runes

I would suggest the following added feature

you can sell purple runes for 1 frag
and yellow runes for 5 frags
Vengeance, Endurance, and Reliability would not be able to be sold

Level would not matter
a level 10 rune would count the same as a level 1