if you cant afford a manager in the first place then forget about it. unless you're a friend of someone who knows these stuff and is willing to help.
bands should start off on their own, marketing themselves and picking up valuable experience on the way.
so when you get big enough as a band, you may want to hire a manager to take care of gigs and evrything because most ppl have lives outside their music. if you get a really experienced manager it could make the difference between a highly successful band and an average band doing gigs in the underground circuit.