An active probe with hi-Z inputs and an amplifier to provide a 50 ohm output isn't cheap.
For the 1S1, I have the P6032 but it's only 850MHz and the plastics degrade quickly and STINK.
Then there's the Type 282 Amplifier.
I have a few lying around. Price is not too bad, this one went for 57$ US.
Then you can find some sort of reasonable probe to hook up to that but of course there are few 500MHz+ passive probes since they usually have too high an input capacitance. Tek had the P6010 that was "wide bandwidth" but even it doesn't quite match the risetime of the sampler, and indeed it depends on the length of the cable.
You didn't say what you want to probe, if it's your own circuits I have put SMBs with a SMT resistor as a power-tap probe. Amplitude calibration is up to you, but you will get quite nice results, if you can live with the stolen power from the signal resulting in a lower signal amplitude. That's why I go for a 1K and use the 1S1. SMB cables aren't too expensive. Mating to the GR-874 is up to you.
