peachcrek, with seven of your folks, I believe the least expensive way to get to/from the port of Galveston is via a limo (no kidding). The one-way seat-in-van transfers sell for about $30 per person and a taxi is about $80 each direction. However, you can rent a limo for about the same amount and it is a much nicer ride...VBG.
There was a discussion about this very topic on here about a year ago and the concensus was that for four, or more people, renting a limo is the way to go. With seven, two limos would be a really cool way to arrive in Galveston.
Have a great cruise!