I have no clue how much a 4 track is in the UK but I bet you could find one online and that would give you a ballpark figure.

As far as operation goes the one I have been using (Tascam 424 Mk III) works by recording strait onto cassette tape.

If you think of a normal cassette tape as having four tracks (stereo Left side A, Stereo right side A and then stereo right side B, stereo left side B going in the opposite direction (I don’t know if that is the right order) all the 4 track dose is use all 4 tracks going one way. Mine records directly to the tape and is very cool !

I paid about 400 US bucks