You can currently watch every film in the "Austin Powers" trilogy on the streaming service HBO Max as long as you have a subscription. A subscription plan with ads costs $9.99 a month, whereas one without ads is $14.99 a month (via HBO Max).
Currently, HBO Max is the only streaming home for the comedies, but the individual films are also available to rent and purchase, as well. You can rent a digital copy of "Austin Powers" and the sequels on the standard digital platforms, including iTunes, Google Play, YouTube, and Amazon, with the price staying consistent at $3.99 each. You can also purchase your own copies and store them on these platforms, as well, with the price remaining $14.99 for each film. Only Redbox appears to be asking more for the "Powers" trilogy at $16.99 per film.
And of course, you can always purchase the comedies through physical media such as DVD and Blu-Ray.