Advice on software selection

I would like to buy an existing software package and modify it so that it will work as the site [login to view URL] does. I am assuming the company did not produce the software from scratch and likely just procured some sort of packaged software and then modified it. So the purpose of this job is for someone to look over [login to view URL] site and then suggest to me the best fit from a pre-packaged software bundle. The software must be able to be run on a Linux machine PHP Language is Preferred. That would be the end of this job. I would then purchase the software and then issue another job to choose someone with experience to modify the package to emulate [login to view URL] If you think it would be better to start from scratch. Then you can send me a note with a cost to produce a functional site from scratch. So this job is to give me suggestions as to what program to use and which one will need the least amount of modifications to achieve a [login to view URL] emulator.