Just like trickster gaia has a function where u can turn reallife dollars into digital items, these items are obtained by either the.
A) Cash Shop.
B) Monthly Collectables.
However unlike trickster you are able to trade these items with other users on gaia using tades or the marketplace.
Since Cash shop and MC (monthly collectables) are for limited time only there is usally a high demand and increase in price the older they become.
As for the shops, (the ones owned by NPC) Their items are known as commons, and their inventory doesnt really change, somtimes they add new items but thats about it. You can usally find discounted commons sold by other users in the marketplace.
I hope i didnt confuse you too much. If you wish to talk about items on gaia i think the best place to do so would be the "Gaia community discussion"
Also the website found at .: tektek.org > Gaia Tools :.
is a useful tool. One of its functions allows you to build yourself a "Dream Avitar" and when you are finished it will tell you the total amout of gaia gold that this avitar will cost you.