I think USPS has the most resonable rates, inside the US or international. Domestically, a 2-lb package costs less than $6 without having to pay for the box (they provide free boxes for Priority Mail) and free delivery confirmation. Heavier packages which aren't oversized may be fit in flat-rated boxes for like $8, also free boxes and delivery confirmation. The packages reach their destination in a few days. You can even use the free pick-up service.
However, UPS or FedEx may be suitable for larger and heavier shipments.
The bottom line: USPS should be among the shipping choices for vendors.
However, UPS or FedEx may be suitable for larger and heavier shipments.
The bottom line: USPS should be among the shipping choices for vendors.