Hi BGCarrera32,
Thanks for being a Stamps.com customer! Regarding WooCommerce, WooThemes has a direct integration - have you tested that plugin? A single site option costs $59.00 and then you must have a monthly Stamps.com subscription that costs $15.99 per month. You can get more info here:
https://www.woothemes.com/products/woocommerce-shipping-stamps/
If that doesnt work, you can import CSV files or even set up an ODBC connection with the Stamps.com Batch option (Batch is the setting inside the software that allows importing from marketplaces/carts) - if you went this route, you could eliminate the $59 plug in cost.
One item I wanted to ask is have you investigated the costs for all types of Priority Mail? Priority Mail Flat Rate boxes are often not the cheapest option to use. You may find Priority Mail Regional Rate Box A or Box B to be much cheaper. Here is a few examples:
5 lb. Package - LA to Seattle, WA (Zone 5)
$11.95 = PM Medium Flat Rate Box
$8.15 = PM Regional Rate Box A
5 lb. Package - LA to NYC (Zone 8)
$11.95 = PM Medium Flat Rate Box
$10.77 = PM Regional Rate Box A
I know car parts can be very heavy, so you probably have already investigated this. But keep Regional Rate Boxes an option for any item under 15 lbs. It is Priority Mail, so it has the same 1 to 3 day delivery option and includes tracking, insurance, etc.
Let me know if you have any questions.
Thanks!
Eric, Stamps.com