Also, you can mix your black acrylic with your white gesso. Do this slowly though so that you get the black you want. Remember, when you add black to white you get grey, so I don't want to see you disappointed when you are not getting the black gesso you want. You will need quite a bit of black acrylic paint. This is a money saver and a time saver so you don't have to run out to the store when you really want to paint.
Keep a running list nearby of the art supplies you need. Sign up for all of the craft stores nearby, so that you will automatically get the coupons online which will remind you of the sales and you can get what you need so much cheaper. Try to be patient if you can with waiting for the sales and coupons. Wouldn't you rather pay $6.00 for a bottle of gesso than $12.00. Your money adds up and you can get another product from the money you saved.