There is an excellent topic at Sphinn asking how do you price your SEO projects.
Overall, many charge flat rates based on how much they anticipate the project will cost them. But some charge hourly. Some charge by feature or service. Most charge monthly.
Let me quote some of the well known SEOs who describe how they charge:
I have been keeping track of my time for all client work for many years, so I have a good idea of how long it takes me to do things for most projects. Since I'm a solo consultant, it's fairly easy to price things out based on that knowledge and the kind of profit I want to make on each project.
A few projects will take longer than I expect, but most go the other way so it balances out in the end.
For the most part, I don't price based on an hourly rate though, but more in what I think it is worth for the client.
We actually calculated our labor costs for 6 months in order to determine what we should be charging for labor for one link IF we buy that link. We have another range of costs for guest posts depending upon the niche, if we go that route. With anything else we do, it's usually a custom cost that depends upon how tough the niche is and how tough the method will be.
I'll admit, my pricing can at times be sporadic for monthly clients. I do keep in consideration my hourly rate and how many hours I estimate I would spend per month on the project. Sometimes you make an extra couple bucks if you overbid but then others you lose a couple bucks if you underbid. I also think its important to keep in consideration your level of interest in the project too.
How do you price your SEO pricing?
For me, if someone wants my SEO advice, I just bill them hourly. Although I rarely give SEO advice outside of this site.
Forum discussion at Sphinn.