Port Aransas is at the north end of Padre Island ,not much difference just more layed back .Lots of "surf shops " etc --condo--motels in area.
Might try contacting:http://www.ccbicycle.org/
I like San Antonio---lots of touris stuff--also great bike path connecting Spanish missions and along San Antonio river.Lots stuff "on the cheep" to do in SA.Missions,Art Museums,Alamo,sometimes mexican Dances,Mexican market,ETC. also lots of BIG BUCK Tourist stuff like Sea World/Festa Texas.
Do some Computer Surfing in these areas and plan your trip---you'll fine there is reall too much to do in a week---you'll just have to keep comming back!