At that budget and year there's a load of good options out there.
Personally wouldn't buy a 1.6tdci Ford as engines a troublesome (engine found in a load of cars including Volvo etc).
Same goes for the Peugot / Citroen 1.6Hdi. Both these engines are economical when they work, but too many issues with them to consider as an option imo. As Graham pointed out the 1.6tdi from VAG is economical, but under powered and feels totally dead (runs out of breath after 2500-3000 and limited power before that) - and have their issues too.
Ford 2.0tdci is a great engine (reliable, powerful enough at 130 odd bhp, and very hardy).
Have an '08 Jag at the moment with that engine and getting between 5.2-5.6 L/100km all the time (long vs short journeys).
It could be got just below your budget. Has Ford reliability, but Jag looks and comfort (PM me if want to know more about the one I have).
Skoda Octavias are great. Very reliable and getting similar mileage out of the 1.9tdi '08 one we have maybe a little better (close to 1000km per tank). Of recent times it only comes in 105bhp form so limited performance though can overtake if needed, but is pretty much bullet proof and economical.
Be careful with all 2.0tdi VAG engines that have the balance-shaft-unit fitted... some are fine and others have issues with the drive key for the oil pump. Which means it will fail between 140-220km - Failure means loss of oil pressure so at a minimum you'd need a turbo and a new or refurbished oil pump / balance shaft unit (a €2k repair at an independent and more at the dealer, plus there might be more damage internally and dpf). That said, apart from that issue they are economical enough and plenty powerful. The 170bhp is a bit more thristy than the 140bhp. The common rail units are a bit better on juice. All the VAG cars are good to drive so whether Audi, VW, Skoda, SEAT... all OK build quality, comfort etc.
Wouldn't personally go near a BMW... again... too much goes wrong, parts are dear and way overpriced for what they are.
If power is not an issue and economy is all that counts the 1.5DCI engine from Renault is not the worst. Just don't buy it in a Renault and consider a Nissan with it instead (Qashqai for example).
Hyundai i30 with the 1.6crdi engine might be interesting as an option too. Engine seems pretty solid like the 2.0crdi that is in your ix35 (stay away from any Hyundai 2.2crdi as it is very soft). Powerful enough for the size car and very economical. Car is not huge, but the 5 door is not too bad and would easily take a buggy in the boot. For your budget you'd probably get a 10 plate - especially come late January.
Hope above gives some ideas.
electrics mainly so stay away from Renault I have yet to see a good 1
