Hello, can anyone recommend a group boat tour departing from Capri for the day that is not super expensive? Thanks!
What is "super expensive?" A boat trip for a full day is not going to be cheap and it will depend on how many in your group as to price.
You can email some of the boat companies on www.capri.net to inquire about prices for your needs.
Oh, so not for a private group that you will be traveling with?
In any case, for what you want, I again recommend you do some emailing. There are quite a few group tour boats that go out from Capri's Marina Grande but they have a set route - around the island; if you are looking for a boat that will stop for you to snorkle, swim/whatever, then asking directly via email is probably best.
There is the opportunity to get a boat for just your party that will go around the island and stop where you like - but, of course, that will be more pricey.