One collectible that never goes out of style is money. If you've got it, you can flaunt it in see-through Plexiglas piggy banks that come in sizes for the rich and not-so-rich. If you've saved $800 elsewhere, you can buy a transparently gluttonous sow, 16 inches high and 15 inches from snout to tail. If you've only got $32.50, you can buy one of her piglets, 6 inches high. They're made by A.R.T.S. in Long Island City, a manufacturer of acrylic decorative accessories, and were displayed last week at the wholesale gift show in the New York Coliseum. Philip Orenstein, who designed them, says the the sow holds about $6,000 in quarters, but adds that the banks are just as decorative when they're empty.