MG ztt 135 cdti. Diesel, 45+ mpg. It was the series of MG built under BMW and as a result, the quality shines through. Make sure you get the diesel as thats the 2l BMW lump, BMW supplied the wiring loom, electrics, audio visual and loads of other bits, including the fuel filler cap!! For 4k, you will get an 04/54 with EVERYTHING on it. good power, good handling. My only caution to you would be the tyre, goes through them quite quickly.
The equivalent BM would be 7k.
Parts are still readily available and will be for years to come.
Since I got my mine, another friend saw it and got one and another friend is looking at one now and looks like he will but it.
Good luck finding one