My billings typically arrive quarterly. I find it very easy to pay the co-payment requirements in return for the prescription needs met.
Veterans in the VA health care system are categorized based upon several factors (service-connected disabilities, former POW's, Purple Heart recipients, non-service-connected issues, and others). The enabling legislation changes from year to year, and co-pays can be adjusted or eliminated for some (or presumably all) categories.
Most years I am billed at a rate of $3.00 per month per prescription provided, typically in 3-month refills so $9.00 per quarter. Some years that co-pay is waived because I am a Purple Heart recipient, some years it must be paid. Any or all of this can be changed by the stroke of a pen on new legislation every year.