You can use standard gelatin (used for jellies) as ballistics gel. It isn't quite the same grade as the real thing, but if you are doing this at home, you don't need extremely exact precision. It's like the difference between 89 octane gasoline at one gas station and the 89 octane gasoline down the street.

As a forewarning, it is still somewhat cost prohibitive. A single batch could cost $45 in gelatin.

Here's the trick: just go to Wal-Mart or wherever and head to the Jello and pudding section. Look for Knox unflavored gelatin or Kroger unflavored gelatin. It should be a little box that is 3" x 2" x 4". Both brands are 100% pure USP gelatin powder. The only difference is in the chemical tolerances for the consumer and scientific market, and even that is probably negligable. You can get boxes that are larger or smaller, just make sure it is gelatin powder and you should be fine.

Get 6 boxes (about 36 oz / 2.25 lb / 1 kg) of gelatin and 3 gallons / 9 liters of distilled water per block you want to create. Then head over to the Ballistics Gel section and follow the instructions there as though you had the ordnance gelatin.