My experience is the bags are generally 24"W x 36" H. It depends on burlap or poly bag etc. Different areas of the country use different bags.
In general, the bags are filled to about 40# if you have civilian volunteers and up to 80#, if the national guard members are involved because they are in better shape than most civilian populations.

If volunteers are used, the cost will be the bags. If you pay people from the "Wagon Yard" it would be what you negotiate. If you can talk a group of Scouts or FFA students to help and give them a badge project or "pond learning project" for a report or essay they might need,it might be cheap.You can ask your "friends" to help and you will find in short order how many friend you really have if you are going to put out a thousand sand bags or more. If you are blessed and have a thousand friends show up,NO Problem", until you have to feed and serve drinks!!! GOOD LUCK and let us know how the sand bags hold up, I am surly curious.

P.S. If you do it all, and your back holds out, you will then say,most likely it is worth whatever can be negotiated, as long as I never have to do it again!!!!

Life is more fun with a pole in your hand.