I'm in center city Jerusalem, where there are probably a dozen new and used bookstores that sell books in English within walking distance of where I live. There are also a few libraries a little farther away with very limited selections. I have at least twice as many books as any of them. The American Consul library stopped offering books at all a long time ago, but the British library in Baka I understand has a good selection. My understanding is that it charges a membership fee, though. The selections in all the bookstores, both new and old, are very, very limited. They never have what I want.
The "free" shipping from BookDepository and BetterWorldBooks really just means they up the price of books to include shipping. If you use a VPN and list the USA as your address, you'll get a different, much lower price. Still, sometimes they have decent prices for books, especially BD with books from the UK. BWB might have that with some old used books.
Amazon has real free shipping on most new books if you order $49 or more for many but not all items. (If you order books from some local bookstores, they'll just buy them on Amazon for you.)
If you're into comics and/or graphic novels MyComicShop sells new ones at 35 percent off with preorders, and you can set up shipping so your orders only go out when they top $50. Their international shipping is $25, so it pretty much evens out. They do an excellent job packing everything, and their customer service is wonderful. But they do only deal with comic books, graphic novels, and comic book novel adaptations. You can also add older comics, graphic novels, and comic strip collections, to your preorder orders if they have them in stock. Prices vary depending on collectibility and condition. (You can also sell in demand issues in good condition back to them, but I don't know how that works.)
Someone recommended AwesomeBooks to me, so I'm ordering 10 used books from AwesomeBooks, and shipping is £11.90. Still, most of the books are 60% off with an additional 20% off coupon code (awesome20 for new customers), so it's still a good deal. These aren't books on my want list, just books they have on sale. The total cost for the order is about $40, so that turns out to about $4 per used book. We'll see if it turns out to be worth it or not.
I hope this helps.