I would not go with the $99 dollar a year, PCI compliant guy. The company I am employed at when I am not working on my side company LOL, actually spends millions each year on PCI compliance. One of my teams does the verification for a large number of our applications.
My understanding is if you have a merchant account, and have developed your own billing systems, then yes you would have to be PCI compliant. If you are using a service to take credit cards for your business, then that company will be the one who has to be compliant.
It is pretty much about protecting credit card data, so it deals with things like when you store credit card data, is it encrypted, do you have the proper controls so that only limited people have access to that data. Do you use a web application firewall or do yearly security testing to ensure hackers cannot get into the applications that store or take this data.
Have all of your developers taken secure coding classes? That is just a few things we have to do each year to pass our audit. If we fail on an item we have a specific time frame to re-mediate the issue or lose the ability to take credit cards and can also be fined.
That is why I doubt the $99 dollar solution is more than a way someone found to make some money. Find business that probably are not needing to be PCI compliant, scare them a little, sell them a scan or something. It feels like snake oil in my opinion.
Here is what wikipedia says about PCI compliance.