Bargain hunters score big when governments give up equipment they bought for plans that never panned out. But officials say that they’re the winners — and that moving to online auctions lowers sale costs, creates a larger audience of bidders and brings in cash for items otherwise gathering dust. In Tennessee, more than 450 governments and agencies sell through GovDeals, double the number of five years ago. Those agencies raised more than $10 million in 2011. All told since 2001, Tennessee sales top $57.5 million.