A pin's worth can be hard to really honestly determine.Some people have formulas which take into account the pins PINPICS wants-to-trade ratio and the LE size,some also add in current and recent ebay sale prices.
I do know of a trader who used an online service which would look up all recent sales of a pin and list the prices and give an average price,though it's a paid service and I cannot for the life of me remember the name (probably not worth it unless you plan to be a pro-seller)
In the end,a pins true value should come from your own personal opinion,with a dash of common sense mixed in.A pin which is worth about a buck on ebay is priceless to me because it was my first ever trade,and some pins that would be worth little $ to some are worth more to me due to personal reasons (perhaps the pin symbolizes a special event or moment).
One bit of advice,if you see a pin you really really like,and you know it's gonna be near impossible to find again,go for it even if it's a little costly.You may regret missing out on it more in the long run than any buyers regret you may get right after
Do a little research to make sure that the odds would be you never find the pin again,and go from there
Probably didn't help you out at all though,just me blabbing my thoughts
