I got a set from Marv Goldens in San Diego for $80.They will mail them to the UK.
They're OK for a passenger and I've had to resort to using them when my Peltors went US.
As to compatibility etc I've never had a problem but you do seem to get what you pay for. The Marv Golden set are about 70% the quality of the peltors.
Has anyone else noticed that compatibility is only generally an issue when a set of Dave Clarks is in the equation.