Write a script for your commercial. An audio/video script is a two column script that has the audio (anything spoken or any sound effects) in the left column and the action (anything the audience will see) in the right column. Script your infomercial in this format using Microsoft Word or a scriptwriting program like Movie Magic Screenwriter. You can also use any word processor that is capable of creating columns.
Make the commercial yourself. You don't have to have expensive equipment to do it. Find a few friends and relatives to be your audience. Ask them to give testimony about your product on camera. Ask a friend to handle the camera work. If you don't have a large audience, the cameraman can shoot to make it look like you do. You don't have to use a lot of audience shots to do an infomercial. If you don't want to shoot the infomercial yourself, you could use a service that specializes in shooting infomercials.
Shoot the infomercial in your house, basement or even outdoors. You can also rent a banquet hall or contact local TV stations to inquire about sound stage rental.
Buy time on a local TV station during off hours. It still isn't cheap, but it is more affordable than advertising during prime time. Consider signing a contract for repeated airings of the commercial, which you can often get at a discounted rate, and your infomercial will run at regular intervals on TV.