Is there a way I can set all shipping free via "USPS Regular Mail"?
All items I would like to offer this free shipping.
Yet I also want to provide users with the option to select a faster shipping, and have Shopify calculate whatever that would cost.
Is this possible?
Solved! Go to the solution
This is an accepted solution.
You will want to add USPS as a carrier on your account by going to Settings > Shipping. Once that's done, that option will no longer be greyed out. After that, you can edit your domestic (or international) shipping zones:
You can go to Price Based Rates and add Minimum Order Value: $0.01 and no max value. Select Free Shipping and you're good to go!