An easy way to get TONS of money: Get rid of all accuracy upgrades and get all the health upgrades you can, then play the first level over and over. You can get over 7000 money with just 4 people maxed on health
Money tips: Try to string up combos, and buy the "Pole Vault" ad use it when you can, you get 1720 style points for using it but it makes you lose a decent bit of speed... I can use it 3 times at the most usually.
I think the prices are fair as is... the first Shopping Cart Hero wasn't short only because there wasn't much to buy, it was also short because you could get all the stuff decently quickly... this has two bosses and tons more stuff than the original.
I won, but because I didn't have enough money at the time, I couldn't recruit the unique Magician... any chance that we have the opportunity to see them more than once?
Guys I'll be nice and say it: The reason that Kong is behind Facebook in updates is because Facebook is essentially the beta release (because of bugs and the like) and Kong gets the final release. I'm on the Kixeye forums (forums.kixeye.com) and I've never seen a bug report from a Kong player, just complaints that the game is behind. Please thumb this up so that people know, and trust me, sometimes these bugs take a VERY long time to fix...
If you can't find secret passages, play through the game. There is an item that lets you see them... I've gotten all the hearts and all but 2 red diamonds by using that object.