Something around 10pF tip capasitance for a X10 probe (10Mohm) is typical. That 10Mohm looks great until you consider the effect of the 10pF shunt at 1MHz which is ~16Kohm
Thaks OK if you are probing a 50ohm line but for anything else that loading probably won't be good.
Personally, I wouldn't spend too much on a X10 10Mohm probe as the results for the extra cash maybe not significant for what you want it to do. The only time I notice the difference between a cheap probe and a much better one is, for example, looking at a square wave when the cheap probe will make it look like its ringing !
RS do a range of cheap probes although the ones I looked at were switched X1/X10
dc