The Disney bus system is designed to get people from their resort to a park and back again, it is very efficient at doing this.
Getting from one resort to another is not as easy, but is doable, it involves going to a park on your resort's bus, getting off the bus and walking over to your destination resort's bus stop and taking a bus returning to that resort.
Since buses can be 20 min.s apart, you need to factor in waiting for 2 buses, plus the load/unload/ride time to the park and the resort. The Disney site says to allow 90 minutes to get from A to B on Disney transportation for ADRs - this is way longer than you usually need to budget time wise, but 90 minutes would mean leaving POR at 6 am for a 7:30 ADR - which is before the buses start running.
BTW, I've only taken a taxi to AKL one time (2010) and it was from the CR, but it was over $35 w/out tip. Not sure how far POR is from AKL. I mention this because I only had $30 in cash on me @ the time and relying on the Disboards wisdom of $20 typical taxi fare thought that would cover it - wrong.