Posting frames

Hello.
I’m currently in talks about participating in an exhibition elsewhere in the UK it’s a little too far for me to travel without a car and thought about posting the Artwork.

Does anyone have any experience sending frames pieces with Royal Mail (or a courier)
if so, how much has it cost you to send various sizes?

I don’t have my frames yet so can’t mock up a parcel, but thought having a few ideas from people that send frames might be helpful in helping me decide what to do.