Speaking as someone who posts from northern Ireland, I've always just wrapped the bass in box really well, rocked up to post office and declared value to them. Most its ever cost me was 50 quid to get insured tracked delivery on a bass worth over a grand.
This is why it bugs me no end when someone tells me to organise courier lol (not referring to poster btw)
YOU'RE selling the bass YOU organise delivery. If I can send it in the back of NI then someone in UK can find their local post office.
I'll get off my soapbox now.
Merry Xmas 😆