Ray Hartmann has written an interesting article for St. Louis Magazine about why the Zoo Museum District ("ZMD") in St. Louis City and County should be expanded to adjoining counties, and why free admission to tourists ought to be eliminated.
He is clear in that free admission should continue for residents of the ZMD since, after all, we are the ones paying the taxes to support the system. However, Hartmann points out that over 50% of the region now lives outside of St. Louis City and County. Tens of millions of dollars would be raised by expanding the ZMD and charging admission to out of town tourists.
In the print edition of the article, there's a chart comparing prices for zoos across the country. A free admission zoo is nearly unheard of, and most zoos charge $15 or so per person for entry. I don't think an admission charge for our zoo would hurt tourism. But I like the idea of starting with a lower admission fee at first - say under $10. After folks get used to it, then slowly raise the fee, a little at a time. Raise it gradually, so that within 5-10 years, we're on par with national averages.
As far as residents of adjoining counties joining the ZMD, that's a different question entirely. Now, they enjoy the benefit for free. Some might consider the free use of the ZMD an incentive to move to an outlying county. So how do you convince people to start paying for something they already get for free? I suppose you do it by giving them a choice - charge them at the gate if their county does not join the ZMD.