You'd be surprised... Hypothetically, if you think you can get $100,000 selling the house by yourself, there is a good chance that listing it with an actual realtor would get you $105,000 - and be less work/hassle for you. Of course that all depends on the market, the neighborhood, and how realistically you price the property in the first place.
The big difference in getting a sale is all in having an MLS listing. Depending on where you live, there may be some alternatives to paying a normal full-comission broker. One is buyowner, there are a few others out there as well. Also some areas even have services that will let you JUST list your house in the MLS for a flat fee. My dad, for instance, is a realtor that offers a discounted comission structure - he will sell your house for as low as $3000 flat or 4.5% of the listing price, depending on the circumstances of the sale. (if other brokers and an MLS listing are involved, the fee is 4.5%... compared to a normal realtor who would charge you 6% or even 7% in some areas). <-- note that this is not a solicitation, as my dad could only help you out if you randomly happened to live in SW florida
Having said all that, it is certainly possible to sell your house by yourself - but there is some risk, at the very least you'll want to have a RE attorney to help you out with the closing contract etc. But you CAN save some money. However, just be prepared to deal with all kinds of BS.
Where do you live?