This is something I just figured out, how much wall street rocks. 5% return is nice. If you set science all the way down and luxuries to a minimum for 10-20 turns, sell off any technologies you have to other civs(I have got 1k gold lump or 100/turn for new tech's before) you can amass 20k gold, giving you 1000 a turn just on interest, with that much cash I could live off the dividends almost. which means for the rest of the game you could almost make it on 0% tax and insane science