My two cents regarding shipping overseas from a USA perspective:
From UK to USA, Parcel Force is least expensive.,
and from USA to UK (in fact to almost anywhere in Europe) United States Postal Service (USPS) Priority Mail International is least expensive.
In my experience, both are dependable.
All shippers have websites that allow you to calculate shipping, but hopefully I can save you a lot of time and wide-eyed outrage when you see the fees that some shippers are charging. Things may change over time, however.
On several occasions, UPS (Uniformed Parcel Smashers) have tried to collect ADDITIONAL "billable weight" and/or customs fees AFTER quoting a price, collecting a fee, and shipping overseas. I suspect it's individuals gaming the system for a profit and not UPS' policy to fleece the customer. In all instances, UPS had all the information they needed when they quoted and collected the fee, and when the package was picked up. Suddenly they have a discrepancy AFTER they have already shipped? Ridiculous! Any discrepancy should be handled BEFORE shipping, and in fact, it should be noted the moment that money changes hands.
From now on, no matter which courier I use, I always take a LOT of pics detailing size and condition of the item, the packing process, the final boxed item hanging from a scale, tape measure showing length, width , and height, etc., and I also take pics and/or video of unpacking something shipped to me. Don't give the bad guys an inch (cm?) or they'll take a mile (km?).
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