Hey there...first off, great idea...I'm a huge supporter of many causes, and giving back, in even the smallest way is a great thing...and needed on so many levels.
I could care less on the item, but many people here, especially the younger ones may be driven by how cool the item is too, even aside from the great cause...so please have the artists do their VERY best (and even better, make it a multi-pose item worked on by ALL the different Gaian artists, as they should all have a hand in it)...
At any rate, while I'm completely okay w/ the $2.50 cost, I've gotta say this...when doing the "Charity" thing, it's ALWAYS (IMO) to go with the lesser cost, whatever that is...go with the MOST accessible cost, because some people just aren't in to donating...so make every donation feel valuable, and encourage even the smallest contribution...so with that spirit, I truly believe you shoud make the item $0.99 in the CS or something...I guarantee you that all the Gaians here with the means and will, will certainly support you TEN fold or more if it's cheaper...I for one, would seriously consider buying at least $50 worth...just for the cause...but it'll also allow those who have very little disposable income to participate, contribute and also get a quality item for less...it's be MUCH more inclusive for all.
Otherwise, when it comes to the cause, all charities are worthwhile..I truly believe that...with that though, it should try to be spread out for the greatest general good, so I'd prefer something like United Way or Red Cross...While Animals are winning, that's fine too...in the end, any of the charities are fine...
I'm not sure though if you could literally pick the top 5 charities and split up the donations and support all 5...you may get less per charity, but you spread the love around more, and support not only multiple causes, but multiple Gaians' causes so people feel better about it by being able to truly choose what they wanted to support in the first place.
At any rate, you MUST proceed with this, it's a GREAT IDEA!