Not looking for anything complex, but just want to check the RAM usage, HD usage, and CPU usage of all of these servers in 1 dashboard. Is there anything out there (preferably low cost)?
If you are looking for something bigger, then zabbix (http://www.zabbix.com/) might be an option. It is not that easy to get running, but has capabilities like dependency based notifications. For example: "Only alarm me of missing ping responses if the router of that box is reachable." I think it is a fantastic piece of software although I had to build an argus-like monitoring interface for it, so that less trained staff is able to work with it.
If you have any questions or feedback I'd love to hear it!
Feel free to give it a try https://nodequery.com/
Feedback would be much appreciated as I wasn't able to gain much traction yet.
It's free while in beta and $60 for 10 servers, so you can try it without paying right now. Based on the preview image, it looks like it's exactly what you want.
Only with curl / or any other language you like you can update the whole dashboard.
Most important of all it is free.
Cacti