Hello, from the site Gaia Online itself:
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Founded in 2003, Gaia Online has grown into one of the biggest forum communities in the world. Today, Gaia is the best place on the web to discuss anime, games, comics, sci-fi, fantasy and anything else you can imagine...
"""
So, Gaia Online is a forum, mainly. Yes, there are mini-games, but certainly is not an RPG, or I didn't found the one you want to emulate.
But you want to build an RPG and say you want it to synchronize users login information with... what? Do you have a forum or something?
Anyway, I'd like to know the details of the thing you want to build, in order to properly assess it and give you a sane quote. So please share whatever extra information you have about this project.
Thank you.