OK, so how do you compute that?
My experience has been with groups of 200 or less and for that two speakers always worked.
The way my Master System is designed, Speakers will change depending on the Venue. I can add or minus depending on venue. Two of my racks (DJ Console/Station) and Process Rack (Includes two amps) are constant. Additional Amp Rack with a 3 way crossover is added when the 3 way system is used.
Two Way System (Options)
2 Bose 802s
2 Bose 802s with 1 JBL Loaded 15 " Regular Sub
2 Bose 802s with 1 JBL Scoop
2 Bose 802s with 2 JBL Scoops
2 Bose 802s with 4 JBL Scoops
3 Way System (Options)
2 Tweeter Cabinets, 2 Midrange Cabinets and 2 JBL Scoop
2 Tweeter Cabinets, 2 Midrange Cabinets and 4 JBL Scoops
I can add/integrate any part of the 2 way system above as fill to the 3 way system.
If needed, for additional sound reinforcement, I will rent bigger or additional gear.
In other words I have approx 10 configurations of Sound Systems. Depending on which one I need to use, I price accordingly as my base price for the System alone. Hours (Anything over 4 hours), ease of load in/out, distance etc will also be factored in to get to the final price.