Small stores probably use retail pricing. To get the bulk pricing you have to be a merchant that ships a lot of items.
USPS rates are the cheapest of the commonly used carriers. All carriers are subject to lost or delayed packages. I believe that favoring one carrier over another is superstition. I've had issues with all the carriers.
You can use the USPS website to see what would be an expected ballpark figure for shipping. For example, 2lbs from US to AU (https://postcalc.usps.com/Calculator/MailServices?country=10013&ccode=AU&m=6&p=2&o=0) shows a range from $31 (First-Class Package International) to $43 (Priority Mail International Small Flat Rate Box) to $64 (Priority Mail International - use your own box) to $82 (Priority Mail Express International). I have shipped bigger and heavier packages and the price goes up a little bit more.
For the bigger packages I have walked into the UPS and FedEx Stores and been given rates of $200 for the one package.
Granted that the time I went for a quote from UPS or FedEx was during the height of the pandemic when all the airlines except United Airlines ceased passenger traffic across the Pacific Ocean. Some freight carriers were still operating. Some commercial airlines operated freight only flights. There was limited capacity across the Pacific Ocean at that time. Now that borders are effectively wide open again, the commercial carriers have restarted their services. There is now plenty of freight capacity. This morning I saw quite a number of flights across the Pacific Ocean.
- LAX-SYD (2 Qantas flights)
- LAX-SYD (1 Delta flight)
- LAX-SYD (1 United flight)
- LAX-BNE (1 Qantas flight)
- SFO-SYD (1 United flight)
- SFO-MEL (1 United flight)
- DFW-SYD (1 Qantas flight)
