Odd. I've never seen cam systems that require a subscription service. Then again, I'm not shopping on ADT's website.
Anyway, I've been tire kicking systems for years. They're available almost every where. Amazon, Costco, ebay, Sam's Club.
There are sales and there are good buys. But in general, the more you spend, the better quality you'll get. It is hard to find systems that *don't* include free internet based monitoring.
Low end:
Analog systems being closed out. Lots of choices around and under $500.
Better:
Power over Ethernet systems. Only one cable to run and generally superior images (higher resolution) to analog systems. Prices start around $800 and can easily climb to $2k and beyond.
Best:
High quality pan, tilt, and zoom cams. Prepare to pay dearly.