Just my 2 cents...
I would spend less of your budget on cameras and more of it on the recording side. Why do I say this? Because if you skimp and buy a cheap NVR, you are likely to regret buying a hard to use, limited device.
I would buy more basic, but still reliable and feature rich, cameras and pair them with a VMS that offers the features and usability that matches your client. Being an IT guy, throwing together a VMS "server" shouldn't be that hard for you. We use Lenovo ThinkServers as a barebone and add in storage. Keeps the pricing down, but is still reliable. Toss on your VMS of choice (we use DW Spectrum/NxWitness) and you are good to go.
Don't forget a decent PoE switch. Don't go too cheap here, or else you will regret not having management features, like per port power cycling, VLANS, etc.
That $3500 budget should be pretty close to buying you 5 x 4MP Hikvision cameras (stay with fixed lenses to save $), the VMS server, VMS licenses, and a decent switch. Don't forget to get matching junction boxes for the cameras to hide the whips. With that cement building, there isn't anywhere to hide them otherwise.