In addition to the tours listed in this guide, you can always opt for a carriage ride around downtown ($25). You can find them lined up around Alamo Plaza. You'll also see pedicabs (bicycle rickshaws) circulating. These don't have set routes or prices, but are generally inexpensive.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.