It would depend on what percentage service connected disability you have to some extent, and which VA region you're in.
If you were diagnosed prior to seperation from the armed forces, your HIV would then be a service connected disability, and any treatment you receive for it would be covered. If not, then the copays, if you have any, are fairly reasonable, and within the vast majority of people's budgets.
As for assistance the VA may be able to provide, they will help with basic medical care (primary care doctor, labs, meds, etc.), vision in relation to HIV infection (it includes full optometry care), mental health care, urgent medical care, and HIV/AIDS case management. Basically the only thing the VA won't do, unless it is a documented service connection, is dental.
If you were diagnosed prior to receiving your discharge from the reserves, I would strongly urge you to see if it can be considered service connected, as you would receive all of the care associated with HIV for no cost to you.