Yes, resales are negotiable - HOWEVER - you also need to be aware that
DVC does have first-right-of-refusal (ROFR) on all sales. This means that once the sellet has accepted your offer they will submit it to Disney who then has 30 days to either purchase the contract for the same amount or allow the sale to go thru.
You might want to look at the ROFR thread on this board which lists reports of sales for each DVC resort over the last several months.
Feel free to offer something less than the asking price, but be aware of the recent ROFR levels to make sure you are in the ballpark. The closing costs can also be included in the offer, so give that some consideration too.
Good luck!