Well, all this stuff is really dependent on many factors, depends on what your clients wants, the time that you have to be ready for a production site, etc, one of the most important factor to take care about is the "pocket size".
Sometimes as a developer you would like to charge a price for the all work and other times is better to have per hour fee, also depends on what is exactly your work, a module that you already know or something that you haven't seen before. Everything is time / knowledge dependent.
The basic functionality + custom template could be around on what Patrick says. For a dedicated server I think a good one for openacs/dotlrn is around $200 +- per month (and maybe this server could handle more that one service). Then you just need to care about bandwidth.
The maintainance should not be to high but that depend what do you call "maintainance", openacs issues and OS issues? or just openacs. The ongoing development is sometimes difficult to arrange (to have a price that do not affect your clients wallet in the long term), and also it depend on what are the future plans for the website.
Note: It all depends! giving you a price without knowing what we are talking about is like saying to a constructor "Build me a wall, how much it will cost?" and you haven't specified to the constructor what kind of materials do you want, what are the dimensions, etc....
I'm very confident that a "lower cost and higher profit" is what should be called openacs and their sons. No matter what, you won't find sophisticated tools like this without licence payment.
