If it's clear that the size of the organization sets the price, you can build price books with that in mind, such as Small (1-10), Medium (11-100), Large (101-1000), Supersized (10001-100000), etc. All products in the price book would reflect the base price for that category. This would make it easy if all products will have the same relative price simply based on the size of the organization and not other factors, such as volume licensing.
This won't work if pricing depends on licensing volume, where they might buy 5 licenses of type A and 2000 licenses of type B (and thus get a discount for B). In that case, you might define a discount matrix. All products would start at their base price, and each line item would be adjusted by a percent value based on the volume. You could automate this with triggers, or manually if you wanted to give bargaining power to your sales associates.
Line items can be customized many different ways, so a specific solution that suits your business needs would best be served by speaking with an expert in a back-and-forth dialog that includes a discussion about your product, your licensing model, how you'd like to view/report this data, etc.