Wordpress itself comes with an installer, and if someone cannot install Wordpress themselves, then they are likely not techie (as the installer is easy) and thus likely needs web design and Wordpress configuring too.
So what you are essentially doing as a "Wordpress installer" is more likely "web design using Wordpress".
I also think it reads more like "software that installs Wordpress", but these things are just IMO. You might get low $xxx from someone who thinks promoting themselves this way would be good. Or maybe more if that is the prime thing they do, install Wordpress and maybe throw a basic pre-made template up on there to get the user up and running.
I'd list it on the major marketplaces (Sedo, Afternic etc) for perhaps mid $xxx bin, or higher and lower it in 3-4 months.
Good luck.