Options for learning HTML include guide books and courses conducted online and through local colleges. Many resources are available for free through online sources or local libraries.
Community and junior colleges often allow students to take just one or two classes and pay on a per-credit basis; they also usually have less rigorous acceptance requirements and charge lower tuition than a state school or private university. Some schools also offer the option to take these courses entirely online or host free online courses that anyone can access such as MIT OpenCourseWare.
Many guide books have been published that allow users to learn at their own pace. Some prominent examples are "HTML and CSS: Design and Build Websites" by Jon Duckett, "Learning Web Design" by Jennifer Robbins, "Head First HTML" by Eric T. Freeman and Elisabeth Freeman, and "HTML For Dummies" by Ed Tittel and Stephen J. James.
There are also a number of online courses hosted by private entities not affiliated with any college. Many of these are free, including courses offered by Codecademy and W3 Schools. These courses may be structured like a college course with multimedia components, or they may simply be a series of instructional videos such as those hosted by Khan Academy.