You should get a tripod before a gimbal, and learn how to set up nice shots with it to capture your truck in different ways. Step back 20 yards and zoom in on it, and smoothy follow the truck as it does it's thing. Some of the coolest driving shots are vehicles pulling around corners or speeding toward a camera in a long telephoto focal length. You will of course be safely on the side of the road, but the squashed telephoto image makes it look like he's coming right at yah!
Or get up close as safely possible, and go real wide on your lens kinda thing.
OR, something ive done, take a seat out of the truck, strap the tripod in there with ratchet straps, have the camera pointing out a window or door with just a bit of the tuck still in frame, and get some cool perspective shots where everything outside the truck is rushing by, but the angle of the camera inside the truck is fixed and still.
THEN you should get a gimbal and try some stuff.
Honestly, if I needed to be a one-man band and had to make a film or other cinematic piece, and I could only have one support item for my camera: tripod. It it inevitably much more versatile than other pieces of camera support gear (unless you have a technocrane or some ridiculous rig) because specialty camera support items only give you specialty shots. But you can get some specialty shots with your tripod too, like the one I described above with the tripod strapped inside the truck.
Handheld and gimbal camera footage get old, and there isn't much craft there unless those techniques are used in specific ways within a greater context. Learn how to shoot with a tripod. Get a fluid head so you can operate smoothly. I suggest looking for a Manfrotto in your price range.
I would love to discuss theory on handheld camera work for films too if anyone would like!