This is probably talked over a lot, but upgraded cards should be less expensive... I am thinking maybe 1000.
It may sound not fair, since established players can farm FGs for ~1100 electrum every card sold, but with the upgrade cost lowered, the selling cost from the upgraded cards would decrease too, so not too unfair.
Many newer players quit after finding out that beating FGs with fully unupgraded deck is nearly impossible, and that every upgrade costs 1500... 1000 would much more affordable...