Sorry to hear abot your Steelie
Unfortunately for you your probably looking for the rarest colour (some will say steel grey is rarest, but i seen 3 of them since november and not seen 1 Candy white one yet!).
Wanting a 3dr candy on 07/57/08 plate with low mileage and top spec limits your options and chances quite a lot.
Imagine 2300 built and equal number of cars per colour thats only 460 white ones, maybe half of those are 3dr so 260, then half of those are poverty spec 130, then you dont want 56 plate lose another 25 or soand your left with 105, and now you want low mileage too
, not too many to choose from.
Above is just an idea and I would say there are way more red, black and silver ED30s than there are white or steel grey although possibly more 3dr versions than 5dr (Lots of ex lease cars will be 5 doors as lots of companies have stipulations on 5drs only).
Chances are with what you want your probably looking for 10-15 cars out of 2300 in the country
Regards how much to pay depends on how hard you haggle, but if i was looking to buy an 08 plate Ed30 I would be looking at £11K to £11.5k, add some for white so possibly £12K max with good spec, maybe more for VERY low miles (remember if your looking for 08 plate 44K miles is currently the average!).
I started looking for my candy Ed30 in June last year and found one in november, in that time on ebay and autotrader I only saw 6 candy white ones for sale. My search was for 3 or 5dr, Candy white DSG, Xenons and sat nav, with FVWSH anything else it had was a bonus!, only saw 2 that fitted the bill and I bought one of them (The other was cleaner but also seller wanted £2K more, now for sake of 2 new tyres, spare key being cut and front splitter being repainted I was happy not to pay the extra £2k for the priveledge!!, it cost me £450 to sort those bits! on mine!)