I bought them all off Aliexpress for between US$90 and US$120 each including shipping. They're all POE (Power over Ethernet), IP66 rated and have really good night vision as well as built in IR illumination.
The Dahua or Hikvision kit is going to beat most other similar priced hands down in terms of actual picture quality. It's not going to beat them in terms of simplicity to set up and configure because they're professional products and aren't intended for the DIY market.
There are a number of identical threads on here including a couple that discuss the Dahua kit.
i would be slightly concerned about the some of the cheap Chinese brands. only use if you know how to secure them. as they do what you want them to do most of the time, but there are some concerns around their security.
there are cameras and DVRs that are easily hackable and few concerns in the professional industry about these brands. even though you change the default password, there is always a master password not visible in firmware that is always the same and can be accessed.
see links below, some of these units out of the box have been known to start contacting servers overseas.
Hey, so how does the software work with these cams. If you have them recording to a NAS do you need the software running all the time? Does the computer itself need to be 24/7 or does the camera write to the NAS independently? I'm looking at the Hikvision range.