Hi King of Elves:
Game size can vary from 4 minis per side (for very elite forces) to more than 12, though any more than a dozen is rare at 500 points (a game that takes about an hour to play).
Most of the time, you'll have 6-8 guys - faction and list dependent. To put it better, if you buy one of the Faction starters and 1-2 blisters, you'll have a 500 PC army. So you're usually looking at less than $100 to get a normal sized army.
Hope this helps!