Toys—even Lego—are damn near free if you aren't picky and will accept whatever you can find used. Often they're literally free. Kids often outgrow toys before they're worn out or broken, and for some reason people hate giving used toys as gifts so there are just tons and tons of them always being dumped on the used market, with relatively little demand.

You could set out with a $20 bill and outfit a 6-year-old with a totally adequate set of toys, from scratch, by just walking a neighborhood on a yard sale day.