You may want to...
...redirect or tap some of the central air ducts and create an outlet near your desk in the garage. Then make sure the garage door and any unfinished walls are insulated on the inside to prevent heat transfer.
A single unit ac under heavy usage will pack about 60-80 dollars to the electric bill every month, maybe more depending on the cooling capacity. As an added bonus it's not nearly as noisy as a room air conditioner either.