You can use GPS without a SIM, but Google Maps downloads the map as you travel, so although the phone will plot your location, it wont show you any roads on the map.
You need a pre-loaded (cached) map solution, such as HTC's Locations app, for one of the many Third Party apps (that I'm sure other members will be able to tell you of shortly), but all of them do have a cost.
If you are happy with a bit of risk, you can type in the route you want to travel while connected to Wifi, and hope that it downloads the whole route and caches it, but if you take a wrong turn or need to travel an unplanned route, it wont be able to help you at all until it gets an internet connection again