I've got a 56 plate 1.9jtdm which I bought two years from new with 20k, I paid just under 14k for it, roughly half its rrp when new. There are lots of issues which can scare at alfaowner.co.uk but yours being one of the latest models with the stronger engine, especially if you don't plan on keeping it over three years should give you less worry.
Lots of the reviews slate that it isn't a useful estate and it isn't particularly, but if you don't need a passat sized estate which a lot of people don't it's fine, you can easily fit an mtb with the seats down and without taking a wheel off. Mpg was a bit disappointing at first, but 44mpg for average journeys is easily possible. 50mpg if you try.
Mine has the 18 inch wheels which have started to corrode at year 6, and apart from routine servicing and tyres up to 40k all ran smoothly. In the last two years I've 'invested' in an egr valve, dpf issue, front wheel bearing, upper wishbone and two coil springs. It had a 60k service last week which was the cam belt job, done at Jamie Porter's, an excellent independent in Royston, there is lots of servicing info on his website.
There will always be the jokes but they've come along way from the 156. If you go for one I hope the dealer is nearby should anything go wrong. To expect a Mercedes / BMW buying experience is ambitious mainly because there are so fewer dealers (and my local one is crap!)