If you don't have G&K, unless you are a hardened civ player who somehow makes everything work (NOT ME), chances are the overwhelming maintinence costs will get to you first before a barbaric neighbor will. It happened to me too, so dont be ashamed. Luckily, I have discovered a great way to keep your economy not only surviving, but thriving. A thriving economy leads to large armies and rapid science achievements. Whether your economy thrives like the rest of the underdog AIs depends on the most important aspect in G&K: Religion. Settle a city ASAP, and research pottery. Then, build a shrine. When you get enough faith, acquire the belief that gets you GPT for each city as your religion, or which ever belief gets you gpt. This WILL yield a gold mine of cash. Also, complete the social policy tradition. Free buildings in cities cut maintinence ALOT and will be very beneficial. Then, make your way to commerce and the rest is history. Be sure to also have an abundance of luxury sources, as these will help a bunch. even if you don't you will still be fine with the religion beliefs. Any other money making strategies will also help, but most of the time, this will help give your economy a lasting jump start. hope it works!