$199 $310
Amazon has the Britax Grow with You ClickTight Harness-2-Booster Car Seat (Cool Flow Teal, E1C199T) for $199 with free shipping. Great Amazon reviews (4.9/5 stars).
Best Car Seat Deals, Strollers on Sale, Discount Carriers
$240 $300
Amazon has the Chicco Bravo For2 Standing/Sitting Double Stroller (Iron, 00079135720070) for $240 with free shipping. Walmart has it for the same price. Sells for $300+ elsewhere. Includes 5-point harness, adjustable canopy, and detachable child tray.