I think the best way to accomplish this would be using a special property of our packaging calculator for the Tube package types (don't worry, you won't literally have to ship in tubes), which consolidate all items configured with Tube packaging into any unoccupied capacity in the largest Tubes defined for products in the same order. I've also figured out how to exclude non-US orders for your $7-shipping product.
First, to offer free shipping on orders over $150, go to Seller Admin > Cart Discounts:
Discount Name: Free Shipping over $150
Discount Codes: [leave blank]
Min. Item Total: 150.00
Discount: 100%
Applies to: Shipping
Click Submit to save the discount.
Go to Seller Admin > View/Edit/Delete Products:
Select an existing shippable product of yours and click Edit;
On the first screen, if Shipping/Buyer's Address is not checked there, tick that box;
Click Next until you reach the Shipping Options screen;
- Weight: 1.0 for the $7-shipping product, or 0.0 for the others;
- Package type - select the appropriate type for the product:
. . Large Tube for the $7-shipping product;
. . Regular Tube for the $2-shipping product;
. . Small Tube for the free-shipping product;
- Capacity: 9999 for all products.
Click Next until you can Submit to save settings;
Repeat this for all your tangible goods;
When adding new shippable products, remember to enable Shipping/Buyer's Address and select the appropriate packaging type.
Go to Seller Admin > Cart Shipping Settings and set up the following:
Shipping Origin: select United States and enter your zipcode;
Shipping Destinations: if you will only ship to certain countries, select them in the list, or otherwise select nothing for Worldwide shipping;
Define Packaging:
- Large Tube: Cost = 7.00
- Reg. Tube: Cost = 2.00
Leave all other settings blank or 0.00;
Click Next to save settings and proceed to the Shipping Rules screen.
In the Existing Shipping Rules menu, select and Delete any Rules you may have saved there.
This rule will allow shipping to any of your Shipping Destination countries only when the $7-shipping product is not being ordered:
Shipping Rate Calculator: Flat;
Shipping Amount: 0.00
Country: All Countries;
Max. Weight: 0.1
Click Submit to save the Rule.
This rule will allow shipping only to the US when the $7-shipping product is ordered:
Shipping Rate Calculator: Flat;
Shipping Amount: 0.00
Country: United States;
Min. Weight: 1.0
Click Submit to save the Rule.
Click Back to Admin, and you're done!