When it comes to cost I think there 2 you really need to look at:
1) Initial cost to get started
2) Upkeep cost to keep the game fresh
So warhammer for instance I find has a pretty heavy initial and upkeep cost. Once you buy your army you can't easily make a small change to change the playstyle or update the army for a new addition. I found I more or less needed to completely redo the army.
Warmachine and Hordes I find has a pretty heavy initial cost now to get started, but I find a pretty light/medium upkeep cost. My E.Thragrosh and P.Vayl have a lot in common, but because of the different warlocks they play very differently.
Malifaux I find has a pretty low initial cost, but it does have an upkeep cost. Might be the factions I play (Guild) or look at (Gremlins), but I find if I want to change the play style or master I'm usually looking at buy a new crew with pretty low crossover with my existing master. Though this could also be a lack of experience with 2E on my part and not using the right pieces.