How to consolidate readings from three diferent machines and bill them together on a single usage li

How to consolidate readings from three diferent machines and bill them together on a single usage line.

eg:

I have three BW (black and white) machines

Machine :  M1

Machine :  M2

Machine :  M3

Reading captured

Machine M1 = 500 reads

Machine M2 = 800 reads

Machine M3 = 500 reads

BW usage line on a contract is with price break

0-1000              : 0.05$

1001 - 99999999999 : 0.03$

assigned all the three machines to the usage line.

How can i bill the cumulative readings of all there machines under the  usage line.

Expected bill should be  1000 * 0.05+800*0.03$ = 50+24 = 74$

is it possible through formula counter, if it is possible how to define formula.