Apple has cut the minimum buy for its iAd mobile advertising platform in half, according to a new report. AllThingsD reports that Apple has reduced the entry cost from $1 million to $500,000, in order to appeal to smaller-scale advertisers that couldn’t afford to initial entry cost. “This new minimum buy is a great step forward and a necessary one, I think,” said Mark Read, CEO of WPP Digital, the digital arm of global ad firm WPP. “Lowering…