So you want to messure the current from a 3.00 Volt 50 MHz source in a 150 TOhm load? Why? And even more importantly 20pA to 100uA is a 67dB range, linear from DC to 50MHz and of course cheap!
The Keysight N2820A has a 3MHz bandwith and it only costs $4,088 the N2821A has a $3,066 price.
If you could only tell us what you are trying to messure, it would be more easy to try and help you.
Johan-Fredrik