from your location Id look up the zip codes of San Diego Calif, Hollywood Florida, Bellingham Washingtoin and Bangor Maine.
Do a sample search on UPS.com and figure out which is the most expensive to ship that item weight to, then use it for all your calculations when offering a part "shipped" to the lower 48 states.
If the part will fit into one of the USPS flat rate priority mail boxes, the most expensive one is the Large and with delivery confirmation, it's $16.95 to all 50 states, puerto rico and guam.