I got my belly button pierced when I was fourteen which means I've had it pierced for three and a half years :) some people may not agree with getting it pierced at this age but I don't think it's any different to getting your ears done. It's something for yourself.
I don't change my belly bar often but here is my collection:

Multiple designs including UV, glow in the dark and flexible plastic. Ebay, pack of 50 for around £6!

The only three which aren't from Ebay haha. First one is from a friend (a gem is missing :(), second one is the one I had my belly button pierced with. It's light pink and in the light it turns multi coloured :) and the last one is what my nan bought me for Christmas.

Ebay, couple of pounds. In between the tear drop and 'pearl' was a butterfly but I didn't like it so I took it off.
Bad quality photo, sorry! Zipper belly bar and you guessed it, Ebay, a few pounds :D I'm currently wearing this one.
Some people might be a bit.. what's the word.. stuck up *cough* I mean worried that their from Ebay haha but their perfectly safe and clean and with any belly bars I get, I still sanitise them.
So there you go!
Toodles my little cupcakes
x