Compared to hiring a local attorney, the cost of an uncontested divorce online is the cheapest and fastest way to end a marriage (as long as both you and your spouse agree on everything). This includes child support, alimony and division of debt/assets. If this applies to your present situation, you will have two costs:
The first cost is the price of your prepared and court-ready divorce forms. You can browse the comparison chart on this page (up at the top) for a complete list of prices; it is generally in the ballpark of $200-$300 for a reputable service.
After receiving your divorce paperwork, you will need to file it. There is no way around this. To file with the state, you will be responsible for paying a filing fee prior to the court accepting your paperwork. This is typically in the neighborhood of $200 but will vary by state.
Note: In some cases, you can petition the court to waive your filing for (for reasons of financial hardship) but this rare and not guaranteed.