Keep an eye out for Army Builders too. Note that not all Army Builders will be labeled such.
Army builders are sets defined by a low cost (5-15 dollars) having lots of MiniFigs (3 or 4 is pretty good, more than that is awesome) and generally a handful of other parts; usually weapons and maybe a vehicle of some kind.
As the term implies, the purpose of Army Builders is to increase your minifig count without spending a crap ton of money all the same time. 10 bucks for four minifigs and a handful of other stuff is pretty easy to meet. Then, when you have more money to spend, you can buy the brick tubs and/or the bigger sets for making vehicles, terrain, and buildings.
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