BRISK BUSINESS AT ARTNET AUCTIONS Artnet launched its online art auctions back in March, and now, more than six months later, business is humming along at a respectable rate. Overall, Artnet Online Auctions have sold almost 600 lots for a total of more than $2.1 million. The top price was brought by Andy Warhol’s print $9, the multicolored grid of nine dollar signs printed in 1982, which sold for $130,000. In addition to Warhol, works by Takashi Murakami and Roy Lichtenstein are top sellers in terms of volume. At any one time, more than 200 lots are up for auction.