The only way to get hokage minato for a reasonable price is having luck on your side and get him in RNG events like lucky snaatcch, lucky dice packs, lucky wheels, missions boxes, etc. You might be lucky and spend a little on these events and get hokage minato or you could be unlucky and spend a lot without getting him so it's a risk if you want to try if he appears. The last time he showed up in the treasure of the sages, the cost of one frag was ~250-260 coupons/ingots. I still do not understand why the Hokages are priced (excluding Tsunade since her skills are meta) like this but it's been like this. Jonin minato is easier to piece since he appears in events where you can get pieces for him for free and the overall price for him is cheaper.

In terms of the future, hokage has skillbooks while jonin has a bond skill from the bond system (which we will get eventually) but you need kid obito and kid kakashi to work.