Power store wont do this, but you could build something like this using the extensions.
Start of with the posting aspect.
Sounds to me like you would want to have the visitors sign in using Security Assist, once logged in they can post the project. the project will be inserted to a database using DataAssist.
Next you would need to develop the system of emailing the lead using Universal Email.
The people that the lead is sent out to will have to come into the site to view the job posting, and input their bid into a bids table using DataAssist.