Are there any commands that I can use to check the router(s)utilization Or any best methodoloy I can use without costs?
At the moment I want to check on a 7206VXR, however, I intend to check other routers as well.
you can use
sh proc cpu | inc util
sh proc mem | inc Free
to have a short output that tells you the current use of cpu and the amount of free memory
You can also use SNMP MIBs to get similar information and to have it graphed for example in MRTG or similar tool
Hope to help