Not sure why the use of paintball. While I have not been part of an urban training program for 7 years, I was impressed with the then state of art simunitions - especially the colored ones that could quickly identify fratricide incidents. You also got a significant reduction in "John Wayne" tactics then you did with MILES - simunitions at least hurt a bit when you got hit.
Unlike normal wax bullets, simunitions are not an inexpensive substitute for live ammunition — costs for simunitions cartridges are as much as three times the cost of live ammunition. Simunitions do, however, provide the most realistic training available.

Besides the rounds, you have to purchase conversion kits for each of the weapons you plan to train with.