You can target U.S. audience by using proxy IP. You can use different VPN services for this purpose. For example, you can use VyprVPN service to access U.S. audience. If you are not familiar with the VPN, you can do research on google. Keep in mind that the more you use VPNs to access U.S. audience, the more you will pay. The payment depends on the VPN service you choose. So I would advise you to choose one of the cheapest VPN services.
Technically, less than $100.
Realistically, at least $1,000 you're willing to lose testing ads to find product / market fit.
If you're drop shipping and just starting out, maybe check out Shopify Compass - there are a bunch of free courses there that can help you get started quick.