The limitation in that case sounds more it would be in th RC car, vs the GPS equipment. You'd have to find one that can navigate the terrain, and support whatever equipment you choose to put on it. But even then, what if it gets stuck? You still have to go in on foot and retrieve it. Is your property really only 2 acres? You could pretty easily do the same thing on foot, probably in less than a day, depending on how close you space your sample points, etc.
Someone suggested the alternatives in the comments:
Hire a surveyor (would probably get you much more accurate data and might be cheaper, depending on what equipment you already have).
Hire a drone operator / buy a drone and fly yourself. You don't need one with LiDAR to get DEMs, there are plenty of services out there with free trials that will generate a fairly accurate surface from photos taken with the drone.