Mazda 5's a lovely car, but that 2l petrol doesn't quite fit in teh fuel-efficient category.
As mentioned look around for some 2nd hand Toyota Versos or VW Tourans. Don't know if they'll fit your price range though.
Honda FRV? although I don't much like the 3 people in the front seat, but you do retain teh boot, unlike most of the 7 seaters.
I've got the 2L Mazda 5 and in town i'm getting not less than 11km/liter
Not too bad in my opinion for the size of car you get.
PS: And too be honest this is hard driving everyday between JHB & PTA in traffic.