The following are basic specifications of network management systems at various prices.  The difference here is that "free" systems require a lot of work and the low priced systems require a little bit of work and the expensive systems require A LOT of work.  It is actually a matter of scaling.  Small systems running on a PC could probably happily manage network of 50 routers and 50 servers with alerting etc.  The free system running on Linux could happily manage 100's of devices but would need a bit more maintenance or an experienced Unix person to make sure that everything is automated.  The expensive commercial system could probably manage 1000's of devices but would need many skilled staff and probably fulltime programmers/developers. 

There is a balance but it can be difficult for most companies to find, balancing initial cost, maintanence time and cost, staff skill levels, staff retention, system complexity, system design and so on.  We will be trying to talk more about Network Management Design and the complexities elsewhere but for now here is a couple of solutions.  Things will be simple, low, medium and high, basic granularity.  A table of Network Management software has been compiled here.