WARNING: "Sandbox" = "Litter box" to every outdoor and feral CAT in the vicinity! (And that includes any area with sand, such as volleyball courts.) Tons of potential for bad disease in there, and NOT just for little ones who don't have great hand hygiene - I'm sure you are aware that bacteria can enter through tiny cuts you don't even know they have gotten yet, especially if they are playing on the playground at the same time. You also don't know what's in there in terms of broken glass, etc.
I strongly advise you to invest in your own - they aren't very costly. To make it even less expensive, or if you don't have a yard to put it in, get the largest shallow rubbermaid container you can find - if Joann fabric has what you need, there is a 40% coupon in the Sunday paper every single week - and use that (you can keep the lid on when not in use, and put a tarp under it if you have to use it indoors to keep it out of the carpet - but obviously a patio or other outdor area is better).
Another idea if you do have a place for a regular sandox is to check the Pennysaver or GreenSheet for someone selling cheap, or advertise on Freecycle for one - if you are not familiar with this, google "freecycle pittsburgh" - there is a yahoo group for it and stuff like that goes through there FOR FREE all the time. The rules, etc, are on the site. You have to post 1 offer before you can start posting wanteds, but even the littlest thing is allowed and probably desirable to someone. :-) After you join, you can look through previously posted messages for ideas if you can't think of anything off the top of your head that you want to get rid of. Good luck and God Bless!