Excellent advice from the person who wrote the book (literally) on web usability. In this article (edit: link broken) he advocates for DIY usability testing when you can't afford to hire a usability expert (and who can anyway?!).
A few things I took away as really great advice:
Do testing one morning a month. Just a morning, and it won't kill a whole day, but do it every month, and you'll quickly accumulate a great practice of getting valuable insights regularly as you work on new projects (or the same old one).
Do testing in person, and get everyone who develops on your team to observe it. There's nothing like watching somebody in person use what you've designed/built. It will give you monumentally helpful insights into how people use your site who are not you!
Just pick three people at a time, and spend about an hour watching each. That will give you a really solid set of issues to discover about your site, and it's not overwhelming when you do just three.