I don't know about the beaches that you are by, But the ones I used to live by, would truck in tons of play sand each year. To help replace the sand that is erroded, and washed out. Plus they wanted a nice clean look for the start of the beach season.
You do not want to put play sand in your tank, Most of them contain silicates which will cause you problem, lots of problem down the road. And even if the sand you find is not play sand, it still contains tons of pollutants. Gas, oils for boats. Sewage that is dumped off shore.(yes they do do this) they dump a few miles off shore. but the tide brings it in. You have people drinking soda, tea, beer. Kids, dogs and other animals peeing in
the sand. Do you want to chance putting all of this in your tank. In two months, you will be scratching your head, wondering why you have all this alge, and why your fish keep dyeing. Just my opinion, but if you are going to spend some big cash in fish, and bring them to your home, you need to do your best to give them the best envirorment you possibly can.