Check your local newspapers and craigslist for aquariums frequently, aquariums are also commonly found for free or for really cheap prices this way.
One thing you may wish to look into is adopting an unwanted ball python from a local rescue shelter.
These snakes are commonly available at animal shelters for a small adoption fee,
We keep our adult in a 4 foot long 55 gallon tank.
Growth is approximately 2 inches per month, so they get big fast growing up.