In the range 400 to 800Mhz there will be many different types of transmission.
Using the UK as an example (you do not state where you are, other than quoting prices in $, but that could be many places.), a television transmitter will occupy a 6Mhz channel, but a radio system will typically occupy a 25 or 12.5khz channel.
So, in one of your monitored segements, there could be 1 TV station or 480 radio transmitters (voice, telemetry etc).
So, what are you really trying to do, what is the aim of this study?
As for using an oscilloscope, not a hope.
Your best chance of producing any results at all would be to use a scanning receiver and have it scan the frequency range 12.5khz channel by 12.5khz channel and when something is received, increment a counter/timer or W.H.Y.
By the way scanning a wide frequency range will be slower than you may like.
JimB