I purchased a 20 Mhz, 450 Vpp 100:1 / 10:1 differential probe on ebay a year ago.
I barely used it as I needed higher voltage and purchased a (expensive) Pintek DP100 (6500V, 100 Mhz) differential probe later, which I am now using - so I can and will sell the other differential probe.
The seller buildt it by himself, the schematic and PCB is based on an article in an Elektor magazine. It comes calibrated and in a housing including a buildt-in power supply and is nicely shielded internally. The full (english) article from Elektor including schematics is available. I will sell for the price I purchased it for which is pretty attractive: Price will be 75 Euros including shipping in Europe for payments via bank transfer. Paypal is possible but will add 3% paypal fee.
Non Europe countries: I can ship to other parts of the world too, probably ~ 10 Euro more for the shipping costs (I have to check first). But you should know that the buildt-in power supply is for 220-240V AV. For 110V you either need to change the internal transformer (2x 15V 3VA) or you will need to connect the supply voltage from an external source.
If interested, please send a PM, I can provide addl. information (pictures, scope pictures etc.) then.