They probably don't. The 20GB tier (now 50GB) costs £0.79 per month in the UK.
To put that into perspective, a can of Coke costs £0.68 in the supermarket.
And anyone who is a bit clever picks up gift cards that are sold 15% to 25% below face value from time to time and uses them to pay.
Are these prices monthly?
Lol at 1TB for $179 in Mexico
Mexican dollars. It's US$10.81.