Can I ask which level you are on?
I remember when i first started and saw something on sale for 1m and was like...i'll never build up enough money for that.... It's hard at first but you have to patiently build up your character base and constantly sent them on tasks to build up my money, then I waited a while before I started mine, got to about 4m ...
If you have unlocked Springfield Heights and got far enough to build beach hideaways, they're good multiplier builders, you get 20% for every fully upgraded one (all the bits have to be out though) ... that can help
But generally you can start now if you like, keep building 10 KEMs and resetting it, that doesn't cost too much and can build up your levels..
I'm just a novice at this so I got my advice off various forum threads, could be worth searching KEM farming in the search box, see what other posts have been made...