I thought you meant some kind of pass-through licensing, but otherwise the expensive stuff like database licenses generally charge per core, don't they? That's going to scale very directly with your number of customers. If you need 4 web server cores and 1 database core per ten customers, then you should not be treating servers as a fixed cost, you should consider each customer to cost half a core and 1/10th of a database core license fee. It's not perfect but it's much much closer to reality than thinking about servers as a fixed cost.
Don't go buy 150 servers in anticipation of customers you don't have.