Dynaudio components can be had around that price second hand.. Keep an eye on Ebay and the "for sale" forum at www.talkaudio.co.uk
If it must be new DLS R6A and Rainbow SLC265 at £169,99 from caraudiodirect.co.uk, both of them are great value for money.
The other brands I mentioned doesn't seem to be availible in the UK (on the sites i know anyways). You will have a greater choice looking at eg. german web-shops like www.caraudio-store.de
Focals in that pricebracket will be the Polyglass 165-v2, also Hertz HSK165 and Helix H 236 Precision are worth a look and listen, if you can find them.
Buying speakers today seems to be a lot of guesswork, as there are very few dedicated ICE shops, and major stores like halfords only sells mainstream brands (from what I can see of their homepage)
The doors are pretty well put together, but the OEM location in the doorcards will get rattely. Get some Dynamat on the doorskins, and cut an MDF baffle, mount to doorframe and mount the speaker to that, this will require the plastic basket in the doorcard to be cut off.
Also sealing off the door cavity with dynamat will do wonders for the sound.
This is what I did to the doors in my old car: