I have been looking into this as well - Galveston Limousine (.com) will get you from George Bush IA for $35 pp, or Hobby for $30 pp. It's anywhere from a 35 to 55 minute drive - depending on traffic. I thought that was pretty good. The price for service from Vancouver Airport to the cruise pier (a 15 minute drive was $26 pp)
Galveston looks like a great place - I'm getting really excited -only 123 days to go
ttfn Jennifer