How close is this Su-27 to the aircraft recording the pass? There is footage of an intercept of a US Nay recon aircraft being intercepted by a Russian Su-27:



(still from the BBC video article, who look like they got it from the US Navy directly)

which was reported on the BBC, CNN and elswehere.

I am not familiar with the proportions of the intercepting plane, but it looks like it passed very close to the recording aircraft! 

Is there a good way to estimate how close it was, to within a rough ballpark? Tens of meters, a hundred meters, three hundred meters?

The CNN article reports that


  Officials so far, have not been able to estimate how close the Russian aircraft came to the US plane, but described the flight behavior of the Russians as the key factor in making the determination the encounter was unsafe.


but 


  The US crew reported turbulence following that initial interaction in which the direct pass occurred. [During the second pass the Su-27] applied its afterburner while conducting a banking maneuver, which is believed to have caused a vibration that was experienced by the American crew.


On a related note, there was also a report of an Su-27 coming within 5 feet (!) of another aircraft earlier in the year; so it seems that this is not a one-off occurrence.
It looks like it's maybe 50-75 ft away from the camera, but you would have to know whether the camera's focal length is neutral, magnifying or wide angle, so it's really a wild guess.  There's not enough detail on the host aircraft to be able to scale it that way.