How can I offer special discounts to foreign customers without letting domestic customers know?

[sin034]

Hi~

We are a select shop in Taiwan

Rencently we want to sell our products to foreign customers

And provides them a special discounts

But in "discounts" page I can only choose the current customers in our website

I want to is there anyway I can auto detect customer's VPN and give them discounts?

(We don't want to let our domestic customers know there is discounts~ )

In the beginning, I want to set different price for foreign customers

And I found the app Multi Country Pricing 

But it's a little expensive and over the budget

If there is a cheaper way that I can show foreign customers a lower price would solve my problem, too!

I hope there is anyone can help me~

Sincere thanks