Audi dealer, $55-$70 i think, but they should have them in stock because we replace them frequently.
I would still recommend you taking it to the audi dealer though, even though the N80 valve is a common problem part.

 

hey, thanks for all the help, i will go buy the part tomorrow.

 

Make sure you take the valve into the parts department, they have different names and codes for each part to be replaced so having it in your hand will enhance your chances of getting the right part.

 

question, i reset the CEL a couple of days ago after i got the small leak code. the light has not came back on. could this mean its fixed because i didnt do anything different after i got the small leak code. any reason that code would come on unless something was actually wrong?

 

There are different stages of leaks recognized by the computer, anything from a very large leak to a very small leak, if there is a very small leak the check engine light probably won't come on for a very long time, or maybe it was something you did like not have the new gas cap completely closed.
The code really doesn't do anything to the engine or performance of the car its simply for emmisions standards so if you have a small leak and the light doesn't come on for like 2 months or so and you can live with it just re-set the light before going into smog testing and they will pass you everytime.

 

If you smell gas in the trunk I bet The seals above the sending unit need replacing. Take cover off in trunk for inspection!!!