Reminder that The Book Depository is owned by Amazon. I hear people recommending it as an alternative to Amazon all the time but it’s not. Amazon bought it in 2011.
Try Hive instead! They give a percentage of every sale to a local bookshop of your choice!
Also bookfinder – you search for a book and it lists all the sellers (both used and new) and their prices from low to high (just generally super useful – also good if you want to sell books and want to check how much they are worth)
You can also try thriftbooks! They have a good selection of new and used books, and the used prices are very reasonable. They also offer free shipping on any order over $10. Shipping is very timely, and their customer service is great; I once did not receive a book I had ordered, and they overnighted it to me the same day I sent in the request to customer service.