How do you get 900000 on gaia?

Currently the most common path users take is investing in a bundle pack from the cash shop when they come up. Usually it's about 10 dollars (9.99), but the items inside give you a chance at some pretty rare items. Rarer items go for millions, other overly common ones may go for about 10,000.
Another good idea is entering a contest, there are writing, design, avatar and art contests. If you have skills you can trade them for gold and items.

The last I'll mention takes the longest but isn't as affective as it used to be since Gaia was flooded with cash items. This technique is investing 2.50 in a monthly collectible letter and hoarding it. Items normally increase in value over time, however as I mentioned above now that there are so many cash items the general worth of monthly collectibles this method doesn't return as much as it used to.