Network Management Software

Can anyone recommend a low cost network management software that can handle the basics like up/down status, check services, keep an eye on disk space and event logs, and can notify via e-mail when a system has gone done or exceeded a threshold? Familiar with the big guys like CA and Openview but way too much. Also love What’sUp Gold’s features but $800 is a little pricey for this project. Looking at keeping the cost under $200. Can anyone make some recommendations? I will award points for any product that meets these criteria. Thanks so much in advance!