invest in forum gold? ...wha? why?
back to the topic - just to give you guys a visual
every El that drops after El slot is at 99 = Eld Rune.
once El and Eld are at 99, every El and Eld that drops = Tir Rune
every El, Eld, and Tir rune that drop when these slots are at 99 = Nef Rune
so you can see the exponential growth as you saturate each slot. my current progression is 99 in each slot up to Hel rune w/ 99 in the Dol slot, so EVERY rune prior to hel is converting into hel rune. (not exactly like this as you need to resaturate each slot prior to your highest saturated slot w/ 2-3 runes for each respective slot, but this is almost negligible as your low runes are just going to continue to power you through!)
Depends where the free upgrades cap at (if hel)
Still like a hundred million to a hundred billion hel runes
If you need gems to upgrade past hel it is silly to consider (silly anyway)
If at 99 it always gives you next rune no matter what this is interesting, if not it doesn't matter.
YOU EITHER UNDERSTAND THE MATH ON THIS OR YOU DONT AND ITS EASY MATH THAT PAINTS AN OBVIOUS PICTURE