AT&T has lowered its pricing on its remaining stock of original iPad 3G units, bringing the cost down to as low as $429. The company is now charging $429 for 16GB iPad 3G units, while curiously pricing both 32GB and 64GB units at $529; the company’s website lists the 32GB model as out of stock, although it’s unlikely that it would have been a popular purchase given that customers could purchase a unit with double the storage for the…