You can add pictures but the admin has to approve them.
In general, no monetary transactions of any kind are allowed to take place on this forum as that would require the exchange of personal information and that is prohibited under the current guidelines.
Having said that, asking the value of a collection is not strictly against the rules.
Nevertheless, having been around the scene for a few years I can tell you that there are no said and fast rules for what something is "worth". The old adage is still true: Whatever someone is willing to pay.
I have often gotten cars for 1€ a piece. I have seen the same car go for 10-20€. I have seen cars go for 100 to 200 €.
I personally don't believe in spending any more than 30€ on a used (i.e. with now packaging, signs of wear etc.) car as I just find that decadent, but that is me.
As gorp said, though he could have worded it more nicely (that is a warning) you have to watch similar items over a long period and decide for yourself.
Prices before and after Christmas always go up for example.