Is a cast net cost effective to save on buying bait? What radius and mesh would work best in the surf?

Absolutely. In the surf as big as you think you can effectively throw, but minimum 5 foot to start.

This is from the TWP regulations site, in the legal devices section.

Cast Net:
A net that can be hand-thrown over an area.
May be used to take NONGAME fish and shrimp only. (See shrimp regulations)
May not be greater than 14 feet in diameter.
In SALT WATER, nongame fish may be taken for bait purposes only.

And yes, a cast net pays for itself very quickly. I personally like one that has heavier weights on it per inch, it sinks faster and seems to catch more fish, although you get pretty pooped throwing it quicker.

I think you should start with the smallest. I think it's 3.5 foot. I can make any of them look like a taco.

+1... I've used nets from the smallest available to 7' radius, and after learning to properly throw one, the larger the net the more effective it will be. I've also bought the whole cost range of nets, from the cheapest to the some pretty expensive ones, and they all are equal when wrapped around a rock. For that reason, I would recommend the nets in the $40 range from Academy, Bass Pro, or similar providers. Good luck!!

6 foot. Anything smaller and you will be buying another one. Practice in your backyard. It won't take long to learn. Youtube example videos. And, yes, you can save money.

I don't know now, but when I lived in Fl, I had a 6 or 7 footer with 1.5lbs per inch, and a 20 footer with 2 lbs per inch.(They didn't have size restrictions back then)

The big one was murder to throw, and you had better get what you want in a couple throws or else you will be ready to go back to the dock. Add the fact that it cost a few hundred bucks, I found myself tossing the little one a lot more.

5 to 12 feet will get you a lot of bait, and I agree start out mid range about a 5 or 6 footer.

I use a 6-7' net. A little practice and you'll be catching bait like a pro.

What size mesh should I buy?

Everyone seems to agree starting with a 5'-6' and practicing catching my dog in the backyard. I had better practice in the front yard and catch kids instead. My part Lab would chew a hole in it. lol

The nets I have seen online have 1lb of weight per foot. Is that heavy enough or should I look for more weight?

They're all equal when wrapped around a rock

That's priceless

One thing to think about is throwing in saltwater I always catch quite a few hardheads, needlefish, ribbonfish etc that can really tangle and tear up a net. But it definitely beats paying the ridiculous prices for bait.

I still prefer the smallest available. I cast around pilings and piers for piggies and croaker. You cant manage a cast net with a 10 to 14 ft diameter in those situations. Those are for open water.

Not to mention your taco shaped cast covers 2 sides of the poles rather than just 1 side, lol.

I like this enthusiasm. I am guaranteed to catch rocks, piers, pilings and hardheads.

What size mesh?

3/8" or 1/2" will work fine.