likes 
If you're looking for some inexpensive sci-fi armored cars, you might want to check the Hot Wheels selection at your local department store.
New for 2010 in the Battle portion of Race World series is the Invader, which is described as:
With twin turbine engines, a turret on top and a big gun, this armored 6-wheel vehicle was made for street patrol with full control.
The model consists of a diecast metal top (painted metallic silver) and a black plastic bottom. The "turret" is cast as part of the body, and sits on an angled casemate (which makes the gun points slightly skyward). There are two hatches on top of the turret, and some sort of bolt-on armor on the turret sides. The "big gun" protrudes out the front and back of the turret, and some kind of brace or locking pin comes up from the back of the car to fit into the back of the gun. The "twin turbine engines" are black plastic. There's what might be an air scoop behind the front wheels, and large dual exhausts just before the rear wheels.
There is some techno-camo on the sides of the vehicle, the toy brand name, and C/3 tactical markings.
Repainting the vehicle might be difficult, as the areas beneath the gun would be difficult to access. Drilling out two rivets might allow dis-assembly of the vehicle.
The Invader looks like it would work with 15mm or 20mm models, and at $0.97 USD (at my local store) could be a bargain.