I think all the hotels have wedding packages that you can customize. My little brother got married there at the Venetian also. Not in the gondolas though. They did do gondola rides later though. It was lovely but it cost them about $3000 to get the ceremony, flowers, hair & makeup, photographer, cake and a couple other small things. They bought their attire before going so that was separate also. I am getting married in New Hampshire in March and its costing us roughly $15,000 (and thats on the off-season 'cheap side'!!) I wish I could have gotten my fiance to do Vegas, that would have been AWESOME!
You can get bridal gowns at Davids bridal brand new for about $200 if you really want to wear a gown. I think Davids is pretty national. They have gowns that convert now too, you button on the gown part for the ceremony and unbutton and take it off and make your dress a shorter dress for the reception or post ceremony bash!