I'm gonna move this to the SW shark and ray section. Might get more help there from SW ray keepers who have large scale pools.
As for the pool, it's an easy build but there is much more to it than building the pool and keeping the rays. For a public interaction area, you need to be up to all of you local public safety standards as well as carry proper insurance.
For a basic cownose touch pool that will be in the public and needs to look good (not just a basic holding pool) you're looking at $50,000 (roughly).
I'd pick Cownose and many Southern stingrays. Bat rays thrive in cold water and leopard / honeycomb / whiptail rays are not only hard to get, but hard to keep and are becoming very expensive. Cownose and Southerns are very hardy and do well with human interaction.
If that's all within your scope, let me know and we can go from there.