Introducing fighting styles and equipment specialized to interact with certain tiles makes life more interesting, to be sure, and can greatly expand the available gameplay options.

My vision here at the moment would be for basic ammunition to be plentiful and free. The whole point in charging for basic ammunition is to remove money from the economy. Money feeds 4 and 5, while adding nothing to 1,2 and 3 and also adding nothing to gameplay. Maybe gaining faction would allow you to redeam a small amount of more advanced ammunition once in a while -- maybe.

GamePlay

In this model, basic game play is low cost or free. Money is made by trading real world currency for a "virtual currency" used to buy perks in the game. Players never "have" to buy the virtual currency, but get desirable perks if they do. The perks are (ideally) limited use, temporary items that disappear after some time. Perks range from simple things (special costume items) to gameplay benefits (bonus experience, reverse death penalties, etc.).

If you look at a Battletech or Mechwarrior campaign, the way it typically played, you started with supplies. You did a mission, took damage, and then you made a decision how to use those supplies to refit and refuel. Supplies were delivered to the campaign at intervals, not after every mission, and so you attempted to salvage as many supplies as possible. I think that design -- a segment of gameplay, followed by a segment of repair, drawing from limited supplies in the segment, episode and series is ideal. It means you have to manage things to keep a high rating.