According to the information I found out, 99.5% Al is the highest quality foil that you can buy, aluminum foils always consist of alloys, 100% Al is not available. With industrial foils, however, you have the advantage of finding an indication of the alloy, which you do not have with normal kitchen aluminum foil.
About the price, I paid for
Industry 1.5kg 29,5cm x 50m, 36µm ca. 32$ resp. for
Industry 3kg 50cm x 50m, 50µm about 63$.
For comparison:
Gastronomy foil 1.2kg 300m x 29cm,13µm about 33$ or
Kitchen foil 128g 30cm X 10m, ??µm about 4$.
So the kilogram price is almost the same.