Was looking at last month's community impact which has a bit of a write up on this.
RRISD currently spends $2,252,384 to local PDs for 23 SRO officers salaries and overtime for on campus event security. They are projecting a year 3 cost of 2,254,541 for a chief, a dispatcher, and 24 officers, with about $600k of that going to equipment, vehicles, and training.
I'm a little skeptical that you can really add 3 personnel without adding cost, but maybe the district is paying a premium to the local PDs or having dedicated personnel that don't also police the community will have an impact on the amount of overtime. But bottom line, the cost of a RRISD PD shouldn't be so much more than paying the local PDs as to require drastic changes to other parts of the budget.