Depending on what your audience is and what your goal in sponsorship is, a few dozen active listeners or thousands, doesn't really matter. If the sponsor sees a benefit then go for it. I've had sponsors from before I even launched several years ago. I approached local businesses, restaurants, bars, and the like, let them know what my show was (interviews of local artists, musicians, authors). We record on site at those locations, and they see an immediate benefit when 10-20 or more people show up to watch & hear us record. Turns an off night into a great night. Worked out other "friend of show" benefits, happy hr prices, BOGO, or other similar for anyone coming in saying they listeners or showing the show web site (with venue logo on our sponsor page). Sponsors for me have been both payments, where we do a straight forward $s for ads on web, social media push, and mentions in show, to trades- free oil changes for all my vehicles, a few sets of tires over the years, a couple of restaurants I haven't paid a tab for in 6 years- show them the benefits/drive customers