The trick is to use a RED+YELLOW tower at the end of your damage chain.
Start off by placing one at a good spot near the middle-end of the map, preferably where it can hit 2 lanes. Then as needed, add towers to the beginning of the map, enough to bring the critters down low for your money tower to get the kill. Use a doll on the money tower to really rack up the points and always be sure its the first to upgrade. Add more as needed. This gives you 30% more towers by the end of the later spawns when it's really needed.
Actually, here's a Youtube video that does roughly the same thing.
http://www.youtube.com/watch?v=PiWWSZiBOww
The most important thing though is to save money for the end. You'll have enough lives to let the boss pass many times. But if you waste your money you won't be able to upgrade. The mages can't hurt the boss.
Skip: For the last level you have 4 boxes. 2 Entry areas, 2 exit areas. There's a barrier 2x between the entry and exit. Stack 10 fire mages along those walls. Upgrade them to 2x Massive damage. Then around wave 14, start building warriors in the boxes themselves starting with the exits. Then finally the 2 entry boxes. Do *NOT* upgrade more than you need, and do not upgrade the warriors too much or you won't have the cash to defeat the final boss
There's nothing wrong with using other games as inspiration. But sadly this is just a watered down version of Evil Genius.
Still gave you 3-stars for effort. But your talent would be better spent on something new and original.
I love this game. Have finished it on many sites. My highest level is 98, and while I'm sure 100-110 is possible (just not for me), how are folks getting level 10,000?