Lahaina Divers takes snorkelers out to Lanai ($69 I think). Because it's a bigger boat, there are lots of places to sit and stand so you can spend time together on the ride out and back, and during the SI. As their name implies, they depart out of Lahaina, but it's a shorter crossing to Lanai than from Kihei.
We book our Lanai dive charters with Lahaina Divers because we prefer the comfort of the big 46' Newtons, it's $30 less per diver (we get a 10% discount from Lahaina Divers), and we know quite a few of the captains and DMs so it's always fun for us. Its a compromise to go with them since they take more divers, but thus far we've never had a full boat to Lanai, the most being 18 divers. <knock wood>