How much to tip for a port?

[caldiar]

When I was first starting out, I would tip 25pp minimum until I could port myself (my main's a druid).
On my alt I tip 50pp minimum, 100pp if I'm in a super good mood or the port is at a weird time of night where most people aren't logged on.
Tip plat is easy to come by when leveling. Anything less than 50pp for a service that saves you from wasting leveling/plat-making time seems cheap to me (unless you're brand new and less than level 30)