To get the inflatomatic achievement, first buy and upgrade the revolver, using all your spare time (when you aren't killing things) to inflate the balloon. As soon as you have $2400, buy the assault rifle, and upgrades, when you can. After that it is incredibly easy to kill all the monsters. I finished in less then 2 days using this strategy. Then play through again just killing everything and buying and upgrading everything to get the other achievements. The same strategy works, just don't fill up the balloon.
@cedar999 You have to hit the targets in the order that they are called out. If you don't have speakers, it is the guy in the middle, the guy on the left, the guy leaning on the apc, the guy near the gas station, and the guy doing inventory.
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