Single shot digitizer.
Memory depth is not the #1 cost driver of those fast real time samplers. Nor #2. Or #3. Maybe #4, who knows.
But I like being wrong, because in this case being wrong is advantageous. Lets go with couple hundred being 512 sample points. Lets go with old school 8 bit, so none of that newfangled 12-bit stuff. The bleeping expensive $100k+ scope under discussion ==> 8 GHz bandwidth signal is to be sampled in real time, 8 bit samples, 512 points. Define far far far less expensive, and rough idea of proposed solution.
How do you propose a real time sampler that can capture that 8 GHz BW signal for 512 points under lets say 1k?
And just to clarify, sampling real time 8 GHz BW signal != 8 GSPS ...