Amazon has the Ripline Epic Series 50' Zipline with Seat (‎RIP.995) for $23 with free shipping on $25+ or with Prime. For ages 8 and up, 250lb weight limit. Includes:

• Trolley with sealed ball bearing pulleys
• Non-slip hand grips
• 50ft 3/16in galvanized steel cable w/ looped eye
• 5ft Sling Cable w/ looped eye
• 6" Turnbuckle w/ 2 eye bolts & nuts
• 3/16" U-clamps with thread cover caps
• 1 Seat and Rope (seat color varies)