If you wait for Black Friday (US) it's half off. If you're a student it's half off.
My Touchdesigner software is twice as much as Resolume. A D3 or Hippo will start you at about $20,000.
So in the grand scheme of things it's NOT that expensive. How much did your projectors cost? You also have to perform maintenance on hardware, you don't really need to for software.
Of course there are other free options out there but you will have to put in hours and hours of work to get it even close to where Resolume's most basic features start, and in my world, time = money