Taken from an AMA:
Any plans to balance fees to rent and summon?
“Currently when you hire you pay the rental fee and then also the cost to summon (as though you owned the hero yourself). Some of the Gen0’s have hit their cap of 30J. As Heroes have later generations and less summons available it will get more expensive. Part of this is that there is a big risk/reward structure where you might get a hero worth many multiples what you paid, but might also have to sell for less than you paid.Frisky Fox, AMA 06/12/21 (link)
We have other things in the works, such as renting heroes out where you can have control of that hero for a few days or a week and pay a rental fee and then have the ability to send that hero on a quest and keep the rewards. This will play into our future foray into scholarship.”