Rinsing with FW with kill off the beneficial bacteria and other life, but that's the least of your worries. Sates, cities and counties spend big bucks replenishing their beaches and will not take too kindly to having you truck off 150 lbs of their sand. If the beach happens to be in a protected area, your legal troubles will be even greater.
Assuming you sneak the sand out a bucket at a time or happen to back your truck up on some dark and moonless night, you then need to worry about pollutants and most of them will not wash out with a simple FW rinse. These would include oils and industrial chemicals. Do a Google search on beach pollution and I think you will see that this is not a good idea.
You'll save far more money (and headaches) in the long run by taking your time, making educated purchases and getting the best quality products you can afford when you make purchases and this applies to everything you buy for your tanks. You migt have to put off a purchase or two while you save up the money, but you'll only have to make the purchase one time this way. Take some of the money you will save following tis advice and put it toward some good, aragonite based sand.
BTW, the aragonite sand from Southdown is no longer available even in Virginia.
