A favorite lightweight/waterproof piece for a lot of folks is the Marmot Precip. It weighs 12 ouncesstill very lightand is genuinely waterproof, yet pretty breathable. And...only $99. Lowe Alpine's Adrenalin Fusion ($70) is competitive with the Precip, although its liner isn't quite as nice. For something very trim, Pearl Izumi's Channel Jacket ($199) uses a proprietary waterproof-breathable fabric and vents beautifully. Or, Sierra Designs offers the lightweight Tempest ($99), which also is waterproof and breathable.
Other than that, there are lots of pieces in that $100 category that offer good but not perfect rain protection, a la the Dragonfly. One good one: The Arc'Teryx Hybrid Jacket ($135) weighs just nine ounces and offers a bit more durability than the Dragonfly.