I guess it's that old perception some people have that if we're from, e.g. the UK, we must be loaded.
It works out as about £5 per hour per student.
That sounds fair for 1-1 lessons but not if you have to listen to 11 others mangling the Polish language!
Why not try to find someone competent who can give you individual lessons? You could negotiate a fair rate if you offered to help them with their English.