Big shout for Conti WinterContact TS830P from me, so good in the cold/snow two winters back that I bought another set for other halfs car last year as well.
Though gotta say they aren't what I'd called cheap, that said hardly worn after two seasons so guess looking good 'value' - and all things relative I guess.
You'll be ok buying 17's - her A4 Avant is on 245/40/18 and they were a fair few quid per corner.