one thing to say, is is it worth considering a mutlicar type policy and getting a tiny little diesel for the thrash to and from work until you move...
if yo ucan leave the 180 layed up at the work car park sorned it could be even cheaper, but then you dont get to drive it unless you take out day insurance etc (or near where you live if you have driveway...)
the cost of selling up to re-buy will always make you loose money imo:
I can see how the fuel prices are killing you with your mileage, but as soon as you move, that becomes more irrelevant doesn't it, and what sort of time frame are you looking at? 1 year, 2 years?
45mpg from the derv is a sensible estimate, but with a little patience, 50-60 is very possible even in my tuned one... as to go at 50mph you hardly need any throttle