I use Royal Mail to deliver my prints and I pop up to my local Post Office about three times a week. Parcels are sent out 1st Class but there are options to upgrade your shipping at the checkout. I can fit up to five prints in a tube so you'll only pay for postage once. If you want more than five (who are you who's been to all these places?) then I'll pay for the extra postage for you.
I really enjoy packaging up my prints and posting them out. When I was a child one of my favourite games was playing with my Post Office set; my little brother was less happy at having to apply for a fishing licence, a passport and a car tax disc every other day though. But here I am all grown up and playing Post Offices in real life. It’s more expensive but a lot more fun.