On my server it seems the general price for anyone who wants a port anywhere is 5g. At leasts thats what they always tip me for anywhere it seems, even Azeroth to Azeroth ports.
As for most people though.... I swear I am going to start charging 15g each soon, mostly for low lvl guild members!! The guild I am in (for.... now....) has been over run with low level "Omg 70's must help me at all times!!" people.
The last 3 ports I have stopped what I was doing and given was from
a: STV.. the middle of it
b: Un'goro Crater... the middle of it, after waiting for corpse runs from Dino's..
c: Uldaman... inside the instance....
My main new rule is, if you aren't in a town, don't ask me! If you get to a major city and ask me.. but I have an instance invite in the 30+ min's it takes you you to finnaly get there, you are just SoL.
I am the only lvl 70 mage.... I just can't stand it anymore!