Getting civilian vehicles suitable for 28mm wargaming is surprisingly difficult.
The commonly available vehicles in 1/43 scale might JUST be ok for 'heroic' figures like Britannia, Devil Dog and TAG, but look silly next to the far smaller proportioned Empress and MoFo figures.
I've decided to treat Force on Force as a 'fun' game which means I still like things to 'look' right, but I'm not going to get too anal about exact scale and compatibilty issues. This is partly due to model availability, partly due to cost (cheap Chinese kits can be had for peanuts whereas a more accurate resin model can be very expensive), and partly because I'd never get a game going if I took too long over everything.
The answer seems to be to find cars that are made to 'fit the box'. It's also very difficult to get 'everyday' generic cars as most toys seem to be Ferraris, Porsches etc- hardly the typical Mogadishu or Baghdad traffic!
I found these models at a local toy collectors fair. Three cars and the VW van cost me £10 (US$16) total, so I was quite pleased.