Since a dozen has 12 items, a half dozen has 1/2*12=<<6=6>>6 items.
Since Jamal bought four half dozen colored crayons, he bought 4*6 = <<4*6=24>>24 colored crayons.
If each crayon's cost was $2, Jamal paid $2*24 = $<<2*24=48>>48 for all the crayons he bought.
#### 48