Any good open source billing applications?

[Maheriano]

I'm looking for a web based solution that will allow me to input costs for materials on a project, specify a markup, input a cost for labour and other items, then have it output a final cost for the project at the bottom. It needs to be a little more complex than this with an admin section to manage the material/labour costs but that's the basic idea.

[firefly2442]

This may be too advanced for what you need but:

http://www.gnucash.org/

I've never tried it but you can probably get the idea of what it has based on the screenshots.