Wireless Microphones
 

I wanted to ask about wireless set-ups. They have different frequencies of carrier wave. Some of the UHF frequencies were made illegal by FCC (frequency C or 700MHz range). I am trying to save some ca$h and buy a used unit. What frequencies are safe to use? (A&B) and what do they translate as far as carrier wave or a channel? Any input welcome!

Both lectrosonics and sennheiser have guides on their websites. It's complex, as every geographical region has different frequencies in use. Also, "channels" are different by manufacturer, you'll have to go by the frequencies.
Although some frequencies can't be sold now, these units are still functional in some areas, and are "grandfathered".
In the end it depends exactly what your budget is. I bought a used Lectro 411/SM kit for $1700 that has been rock solid. It was my 3rd wireless, each more expensive than the last, with a mediocre UHF destroying a corporate event once as my last bad experience.