Water damage isn't covered under warranty and given the water sensors are near the speakers, I'm guessing they will see the fact it's taken a swim in wine pretty quickly.
From my experience I'd take to to Apple and be up front. Chances are they'll offer you a cheaper replacement.
With that price in mind you can then take it to other independent repair stores and ask how much they'd charge. The part itself is cheap to buy. Plenty available on eBay. Taking apart the iphone 4 isn't for the faint of heart though.
You could always take it to them and see what they say - you may be able to pay for a repair.
That said, when I went in because the microphone had gone on mine, they asked no questions about how it happened - didn't even look at the phone - they just asked me if I was backed up, took it off me and handed me a new one.
I dropped my iphone in ... well okay.. not water exactly.. but a vat if fermenting wine. The sound has now gone (tho works okay thru headphones). It's less than a year old but not insured. If I took it to an applestore, do you think they'd replace it free? Or do I need to buy a new one? It was completely my fault.