Ttere are 3 ways to get from the airport to your hotel. The 1st is a water taxi and you are right about it being the most expensive. Probably 125 Euros for the boat. But there is now a shared water taxi that is (I think) somewhere around 28 Euros per person. Do a google search and check it out.
The 2nd and next least expensive is the Alilaguna boat. It will cost about 20 Euros per person. It takes longer, you do have to "check" you baggage so you don't have control of it the entire time, and you probably will not be able to get a "non stop" line to the area of your hotel.
The 3rd and least expensive is a combination bus and vaporetto (vap.). It takes a bit longer, but that is what we do because we travel very light with just one carry on apiece. There are two bus lines that serve the airport. One is ATVO and is NOT affiliated with the vap. system. The other is ACTV and IS affiliated with the vap. system. At the airport you can get a vap. pass for various periods from 24 to 72 (or more?) hours. You can have a one way or two way bus fare added to the vap. pass. There is a good site maintained by the ACTV system that has current prices and etc.. Don't remember the url so just Google it.
If you decide on option # 3, take the # 5 ACTC bus from the airport to Piazzale Roma. Be sure and validate the vap. pass on the bus. Do not wait until you get on the vap. Also, validate the pass each time you use the vap. Then take to the vap. to the stop closest to your hotel. The # 1 vap. is the slow boat as it stops at every stop and the # 2 is faster as it only stops at selected stops. Either one will take you to the vicinity of your hotel. We've done option # 3 many times. Easy Peasy and cheap to boot.
There is a site called veniceforvisitors.com that has a lot of good info. that you might want to check
