For an accordion aficionado, walking into Boaz Rubin's Berkeley shop is akin to stepping through the Pearly Gates. The front room of Boaz Accordion's walls are lined with new and used piano accordions, button accordions, concertinas, sheet music, and accordion paraphernalia, while the back room is filled with tools of the accordion-fixin' trade. The shop's Squeezebox Theatre offers frequent concerts and lessons, including Wednesday night drop-in sessions for beginners at which Boaz and musician Henri Ducharme take turns teaching button box and piano accordion respectively. The hour lesson from 7 to 8 p.m. is only $15, and instruments are provided for newcomers. The squeezeboxes for sale range from several hundred bucks to $10,000, and Boaz even sells his own invention, a nifty, medium-sized Italian-made beauty called the Blue 72. And if busting out $10,000 to buy a top-of-the-line Armando Bugari is bound to break your budget, there are always toy accordions -- they go for $15.