How bad is the movie biz? Well, now they're giving away free popcorn. The common wisdom in film exhibition has always been that you sell tickets however you can, then score a profit selling overpriced popcorn and candy at the concession stand. But Renaissance Rialto, operator of Oakland's ornate Grand Lake and the attractive Art Deco Orinda, is trying out a new strategy: free popcorn Mondays through Thursdays at both movie houses. For Renaissance Rialto boss Allen Michaan, it's a bit of a desperation move. "We're doing it strictly to try to get first-time visitors into the theater," he explains. Both the Grand Lake and the Orinda are elaborate throwbacks to the movie-going experience of 50-60 years ago, an alternative to multiplexes. "We have no commercials, no video games in the lobby," Michaan says. But a combination of home entertainment and the big circuits are gobbling up his customer base. Complains Michaan, who also operates Antiques by the Bay, his antiques auction business in Alameda: "Our audience is declining at the same time our costs are rising." So now it's popcorn on the house. What's next, a set of dishes?