One quick google away:

> Can I really pay with cash?

> You bet, and please! Stay anonymous all the way. Just put your cash and payment token (randomly generated on our website) in an envelope and send it to us. We accept the following currencies: EUR, USD, GBP, SEK, DKK, NOK, CHF, CAD, AUD, NZD.

https://mullvad.net/en/pricing/