Instant upgrade is available free of charge to blue, silver and gold skywards members. Requesting an upgrade at the airport/aboard is only valid for the flight segment to be taken (not subsequent flights) and hence will cost more miles in a multuple leg journey.

Generally you should not pay a penny more, unless there is difference in airport taxes (it happened to me several times).

I am not sure where you got that $50 from. Get your info right jetsetkiwi. Oh that's right you're still a skysurfer :P