All Spearthrower said is very good advice (although he did say he upgraded his starbase), and yet I find it very odd that your 35 planet empire gained a net of 530BC with an economic boom and you said you have lots of econ planets. Usually I can pump out over 2000BC per week during events like that, and I never play on gigantic (takes too long), so I only have around 20-30 planets max. The only thing I can think of is why the heck are you using advance marketplace. Generally I rush stock exchanges really fast. I mean you have 35 planets, you should have had plenty of time for that, if not that, at least trade or banking centers... if only for the econ bonus the tech gives alone.
That aside, I'm pretty sure whenever your planets rebel, they give you 10K. It's like a "hey, thanks for keeping us alive til now, we don't really like you, but here's 10k, please don't kill us" fund. That's why you have money. Unlike Spearthrower, I don't think your poor economy could have pulled out 10k in a few turns. I also don't think it was a random event. This seems to be a low morale situation. Whenever you're in the red (in debt with negative treasury), you suffer a morale and production penalty. The longer you stay in the red, the more this penalty applies, until when you reach -2000BC, where your economy stops completely. EVERYTHING, research, production will say "never" when you have -2000BC. This will last until you have positive money again.
Oh, and that +10 trade ability is a complete waste. I often get more out of tourism than I do with all 10 trade routes going at once. It seems like trade REALLY needs a boost. Back in GC1, I remember trade was so important, I couldn't afford to go to war with people. Now, it's such a trivial matter, the only reason to trade is to keep relations up with people you don't want to fight just yet.
Because trade is worthless, economy starbases actually doesn't HELP your economy any. Insteady, economy starbases only help production which means it costs you money. So before you go around sticking economy starbases everywhere, keep that in mind. The only places you should put these things is around your manufacturing centers. The most I would put anywhere else is 1 to help them build their improvements and lower the amount of factories that you have to build.
So give what Spearthrower said a try, but if all else fails, and you just CAN'T keep your money up, use the cheap strategy, buy/trade for techs, and sell it to everyone else that doesn't have it. You'll be filthy rich in no time. Although it might not be so fun anymore.
