For years the Villages Golf Carts sold Ultimate Seats out of Indiana I believe. I got them on my new Yamaha in 2011 and they were installed for $1500 when I bought the cart.
I believe Ultimate Seats went out of business and now The Villages, last time I checked, were selling and installing El Tigre Seats. They're very similar, if you order from their website this is $1400, or you could buy from The Villages and have them installed.
Pages Archive - El Tigre Custom Golf Cart Seats | Golf Cart Seats
Villages Discount Golf Cars on 466 just east of Morse in the tan shopping center next to Birdie Golf specializes in selling recent Yamahas refurbished with Villages upgrades for $8,000. My neighbor bought one of their carts and has the upgraded seats. They're nice, they just don't have the center armrest like my Ultimate but do have seat belts. They would probably be cheaper. They sell an package for $2500 which includes the seats, mirrors, sunbrella, mats, turn signals, headlights, everything you need. They probably sell the seats separate. This is their refurbished carts with seats.
Village Discount Golf Car