Sand in the body? Probably best bet if one of the dusters don't work is send to manufacturer, is it on the sensor or just in the body? Most solutions that are used to clean the sensors can't be shipped by air, so they are rough to clean, not to mention very fragile.
It is okay to shoot at the beach in the wind, just be careful. When you are at the beach never change lenses and make sure you have a UV filter on the lens. For me when I'm at the beach I only use my 50 f/1.8, The lens is less that $100 so if it breaks it doesn't kill the wallet. Right after you get home pull the battery out of the camera and gently wipe the body down with a damp rag (not a lot of water), do the same with the lens. Then soak your filter in a bowl of water, that'll remove the Salt residue, then use some isopropyl alcohol to clean the lens filter so you don't get water streaks.
If it is really windy I usually cover the camera. Take the stretchy-est sandwich bag you can find that is roughly the size of camera and lens, cut the corner off it then stretch it over the whole lens and have it cover camera body. It should be pretty hard to stretch over the lens, very tight. That'll keep the flying sand out, and you can clean your sandy paw marks later. Only rough part is that on windy days the salt gunks up any lens cleaning rags so within an hour there is no way to get the salt smear off the glass and any sand on the rag can scratch glass. Make your windy beach trips short and do a good cleaning when you get home rather than at the beach.