For that budget you're looking at the cream of the E46 crop, perhaps even sneaking into smaller capacity E9x territory.
Beware the engine designation thing. 'Trader is right that some 318's are listed as 2l. Similar to mine being a 335d. It's only a 3 litre but has 2 turbo chargers as opposed to the 330d's 1, hence the additional '5'.
I wouldn't say your mileage necessarily warrants a diesel (that is unless you like the way they drive). A very nice 330i is well within grasp (and will return a steady 30mpg if driven nicely), indeed (dare I say it?) good E46 M3's now drop in below £10k.