travel from marco polo airport to Hilton on Guidecca

Yes, the water taxis are very expensive. According to one guide book, 80euro from the airport. Apparently there is a blue ATVO bus that for 3euro makes the 20 minute trip to Piazzale Roma. From there you can take the vaporettoto anywhere in Venice. The 41, 42, 82, and N lines make three stops on Giudecca. It is likely that the 41 runs one direction and the 42 in the opposite. It appears that the N line may be a late night only run. I don't have a large enough map of the vaporetto routes and all of the lagoon islands. In any event, one of the above lines should get you there. It would be wise to search for a full map of the system to see whether you want to go clockwise or counterclockwise.

Very easy and inexpensive to do. First, take either the ACTV or ATVO bus from the airport to the Piazzale Roma (6Euro or less). From the Piazzale Roma, take the No. 41 vaporetto to the Palanca stop. David is correct that the 41 and 42 have the same route but they go in opposite directions. If you take the 41, you go about 3-4 stops. If you take the 42, you'll eventually get to the Palanca stop but I'm betting it will take an hour longer. A single vaporetto ticket is 6.50Euro or if there is a Hellovenezia booth at the Piazzale Roma, you can buy a 12,24,36 or 72-hour pass.

Do not get off at the Saint'Eufemia stop. There is no direct access to the hotel from that stop even though it looks like there is. Trust me, we did this thinking the stop was closer to the hotel. It's not. Even from the Palanca stop, you have to walk about 1,000' and across two canals to get there. Bumpty bump with the luggage. You'll LOVE the hotel, however. It's a converted flour mill (Molino is Italian for mill). It opened a year ago on June 1. We were there.

The hotel has it's own private dock. The vaporettos don't stop there but the hotel has two private shuttles to both Zattere (across the canal) and a private dock near San Marco. No cost for the shuttle. They depart every 30 minutes during the day from each of the two docks.

A water taxi from the airport to the hotel will run you about 100Euro-115Euro ($150-$172) for up to 6 passengers. It will stop at the private dock.