Left Monster legend and playing Dragon city .
Im a total newbie but still the runes arent that expensive (at least not in low levels)
you can make a level 10 rune using Ingame Gold heres the pattern :
Lvl 1 * 4 = 2Mil
Lvl 2 * 4 = 8Mil
Lvl 3 * 4 = 32Mil
Lvl 4 * 4 = 128Mil
And a level 6 Rune would cost 512Mil .
For me its a lot , For you I dont think its more than 10 $. (if you are level 100)