There are two primary companies that are doing video-centric central station software.
The oldest is SureView, with their Immix product. Most central stations use Immix alongside an automation platform like BOLD Manitou, MicroKey, etc., but it can be used stand-alone if you're not trying to do traditional burg/fire monitoring.
The other primary company is iViewNow.
Pricing for both options varies between the monthly per-device cost, initial setup, etc.
Immix is probably the more robust platform, iViewNow is a little cheaper and sometimes easier to work with.
You're going to have a rough go of it (IMO) doing motion-based monitoring. You will get LOTS and LOTS of false alarms. Some products are also better than others at generating alerts that can be easily routed into some kind of automation platform. You may need to resort to kludgey stuff like hooking digital outputs into an alarm panel and receiving the event via the alarm panel.
I'd suggest going to the upcoming ESX show in Baltimore, which revolves around much of what you want to do.