How many salary surveys does a 300-person company really need?

I am a people operations manager at a 300-person software company with offices in Amsterdam and Berlin, and compensation became part of my job this year. We are growing by about 80 people a year, mostly engineers and sales.

We currently pay for one survey and I have been quoted for two more. One of the salespeople told me that everyone our size uses three. Our finance director wants to know why one is not enough, and I do not have a good answer either way.

What do companies of our size typically use, and how do you decide whether an extra source earns its place?