Good idea and agree with Bjarky to make it optional and dependent on gold, not lvl.
Also, maybe add another peasant ticket, with almost no upkeep for it? Would also like to change the other lvls a bit.
Like:
Peasant, lvl 1-10, almost 0 upkeep, even for large groups of them. Not like having many 1-15 players is gonna help you.
Militia, lvl 11-24, useful lvl, but still not "proper" soldier lvl. Has some basic upkeep.
Soldier, lvl 26-30. The lvl area where most builds are fully usefull. This is what would be the "basic" ticket and where most people would take from. Upkeep on these should be the upkeep we have on tickets now.
Elite, lvl 31+. Highest upkeep of them all.
The reason i put lvl 30 in soldier ticket is because that's where most people are gonna be (retiring when they hit 31) and thus lvl 30 shouldn't be the "elite" soldiers. Those who don't retire anymore to reach a higher lvl and become better in strat should be the "elite" tickets, while the "soldiers" are when builds are finished/close to finished.
Another thing we can do is to not have the tickets lvl dependent, but make better tickets give bonuses. Like, peasant is just your normal build. Militia gives +1 ATHL and +1 PS. Soldier gives +2 PS and ATHL, a +1 shield and +10 wpf (in all). Soldier gives a +2 to PS, ATHL, IF and SHIELD, +1 to PT, PD, RIDING and HA and +15 wpf. Veteran gives +3 to PS, ATHL, IF and SHIELD, + to PT, PD, RIDING and HA and +30 wpf.