Better to balance the equipment rather than rely on deterrents like upkeep. If you don't want too many people using a particular item then give it adequate downsides to using it. Instead of making cav really expensive make it so there are more negative elements involved. The heaviest horses should be cheaper but not have so much HP/armour etc. Arbalasts should be more than point & click, and you should have more downsides to equiping one. We have the slot system to tweak with as well.
It goes the other way too..there are plenty of overpriced melee weapons and body armour that don't really justify such a price tag. Heavy armour isn't necessarily better than medium but its more expensive. A Flamberge isn't better than a Longsword, its just different. Having lots of Flamberges won't unbalance the game more than lots of Longswords
