That seems steep - here A 4000 Report-L will be around £50, although a good serviced one will likely be more. Unless it's one of the later Report Monitors, which are sometimes stereo and have become one of the collector's fads, with the correspondingly inflated prices.
The 4000 Report-L is two track, so half the tape is used in one direction, the other on the way back. I'm not well versed in tape formats enough to be specific, but perhaps the tapes were recorded in 2 channel 2 track, but played back on a 4 track machine, so you get half the track from side 2 while playing side 1.
Look at this diagram to see what I mean. Obviously it would be best to play it back on the same sort of machine it was made on, so you don't lose half the information on the track by using another 4 track machine, the head of which will only read half of the 2-track when playing side 1, as you'll have to mute the channel that's reading side 2 at the same time.