There are many flat-fee services that offer minimal service, but will put you on the MLS for as little as ZERO dollars, on up... Some limited-service agencies will charge a minimal commission (maybe 1-2%) but have you do most of the work. Some agencies will rebate a portion of the buyer's-side commission to you, and offer limited services, and then there are full-service agencies, whose services run the gamut, and so do their commissions.
I had a client who told me that the standard commission in Chicago (yes, she meant the entire city of Chicago) was 5%, because she had spoken with a half dozen agents, and that's what they'd told her. I personally know full-service agents who charge 4.5%, and I know agents who routinely get 8%... both sets of agents have regular repeat business, so their clients must be happy.
There are lots of business models available for real estate agents/agencies... you just have to decide how much of the work you're willing to do yourself, in order to save some money.