Haven't checked the links so don't know if these have been suggested.
My employer had me meaured for some ear plugs as an alternative to the foam squeezy ones! Bloke came down squeezed stuff into ear and ended up with a cast of my outer ear canal.
Two weeks later was given two sets of clear plastic plugs. Funny looking with a little sort of open vent in them. I wear them 9 hrs per working day riding a motorcycle without problem. Wind noise drastically reduced. The siren I'm sat above even sounds bearable, yet take the lid off and I can still hear a normal conversation perfectly without removing them.
Bloke tested them by sounding a rape alarm. Was really strange could hear the thing beeping although quietly and could also hear his voice at normal volume.
Don't know the tech stuff but apparantly they cut out/down certain damaging noise levels but leave the rest unaffected. Plastic tube thingy is vented so would also be ok with pressure changes.
Not tried them yet whilst flying.
No idea of cost, but I am aware company keep the casts so replacements can be easily made.
If anybody is interested I'll try and find out who made my set and how to contact them