Try not to smash your computer...

On Stage 4. The trick to it seems to be diligent use of resources. Your base will take some damage if you cannot create the Yee-haw points by destroying enough zombies. You need to build as many salvage yards as allowed and then build the larger buildings. If you can achieve at least one good Yee-haw power or can wait it out to a larger one, like that horribly destructive combine truck, then you can keep on racking up cash. The zombies don't stop coming till their base or yours is destroyed. It seems unfair that the zombie side can push out so many units so quickly and the only means to compete is to produce the same or similar amounts of violence. If you can get the Garage and Survivalist, you can put up more of a fight. The Preacher is pretty cool but ultimately expensive. You can adjust the speed of gameplay and that may work to your advantage or disadvantage as you may see slight increase or decrease in certain gains or losses.

I used this strategy. Wait until you have 500 (don't spend any in the beginning) and buy a supply thing then you wait til you have 250 again (the zombies will begin attacking your base right around then) so you make five guys and as a group they take out enough zombies for you to make another 500 and buy another supply thing, increase your total to ten guys then do the process til you have all the supplies. You should have quite a bit of yee-haw so use it when zombies get right next to your base while you increase your total to 50 people. Then save up for the barn or farm house or whatever and while using any yee-haw powers that become available make an army of 25 farmers and you are set. I only made it to 20 farmers and i won easily but expansion is always good. You don't need any of the other guys just farmers.