A D-Sam 6000 would cover most everything you need and a lot more, just plan on spending some time learning how to use it.
If you just need a meter that will give you a modem lock to verify that the return is working look for a used Trilithic DSP 860, it gives you decent MER/BER capability as well as Docsis test.
If you plan to stay in the business and move on to better things, go with the Dsam.
