Do you think the numbers make sense ? The cameras they have -16 with res 480, 30 with res 720, 21 with res 960 , and the rest are 240. I can get new cameras with an nvr with about the cost of licensing. The maintenance guys sit around so screwing in the new ones would just be utilizing the labor that they are already paying for. There would be some cost of programming but they would have much newer cameras.
Those are some pretty low resolution cameras. What are some of the model numbers of the cameras? Do you know how old they are?
You're not really giving us a lot of information to work with. What are the intended purpose for the cameras? Will someone be watching the live stream constantly? Do they need integration with a POS system, access control system etc.?
74 cameras is a lot and will consume a considerable amount of bandwidth. You can't just go out and buy any cheap NVR and slap it in there and hope it'll work. You need to plan and design system taking into account resolution, bandwidth consumption, storage requirements, network topology etc.
This is a large system and you should really be using an enterprise grade solution like Axis Camera station, Milestone Xprotect, Digital Watchdog Spectrum IPVMS etc.
You mentioned money is an issue. How big of a budget do you have?