In a major city, the average retainer, which should suffice for the whole case, is $5,000.

If difficulties arise, it could go up to $10,000 finally, but this would be considered high.

In smaller cities and communities, a $2,000 or $3,000 fee would be more typical.

A country lawyer might charge only $1,000 or less.

These are fees with children involved, but no big fights over wealth or substantial real estate.

If there are no children involved and no fighting over money or property, a do-it-yourself job would suffice. But still you pay filing fees, maybe up to $300 more or less.

In all honesty, it varies. Cost can vary depending on location, the complexity of the divorce (eg, if there are lots of assets involved), the experience of the lawyer, etc. In most instances, I would anticipate that any halfway decent would ask for a retainer (probably at least $5K in major cities) and would have you sign an engagement letter that lays out the anticipated costs (court costs, copies of docs, etc.) and fees (what lawyers and their staff will be paid per hour). This may not be the case in smaller cities or rural regions. (By way of example, I have a friend who practices Family Law in a major city, and her minimum retainer is $5k. She figures that if they have trouble getting their hands on that, then they will eventually have trouble paying the bills.)

Regardless, I'd be wary of any "flat fee" lawyers offering to handle the case for a fixed amount. They will often spend just a limited amount of time on your case, then will do very little because they aren't making money off of you any more. For instance, if a lawyer typically charges $200/hr and offers to handle your divorce for $1000, you will probably get about 5 hours of quality work out of him ($200 x 5 hours=$1000). After that, every hour he spends working for you is costing him money.