I just moved from Raleigh about 8 months ago.
I spent almost 6 months trying to find a rentable and large enough garage space.
You have two real choices. For ~400 bucks a month, there are a number of small (900-1200sq ft) industrial park places in Garner, Wake Forest, Holly Springs or Apex. All I ever found were about the same size: 20x40, or thereabouts of usable space. All I found also included electricity, and the few that had it, heat.
For ~1400 a month you can get NICE, HUGE warehouse spaces in Raleigh proper. I'm talking anywhere from 2500-6000 sq feet. Most are now prewired for 220, and are setup for industrial shop moveins. You will have to pay power and everything else in these spots. Much more expensive, unless you go in with a couple of buddies to make it a "community" garage.
The last option, and the one I'd consider if you will be in raleigh for another 5+ years, is to buy an empty plot anywhere in the area that's zoned for it, and build your own 5/6 car garage. All total it'll run you 35-45k, and will be a guaranteed positive return on your investment to rent it out or sell it down the road.