Depends if they actually need rebuilt or just cleaned. Just as a reference I had pulled off a carb block off a '78 kz650 that I restored and had the carbs rebuilt. That included new seals, orings, gaskets, sync'd and bench vac tested. The total on that was $180 and they came out better than new. So if you can do that, new seat, new tires, and cost of bike, you might be into it for under say $1200. Good deal.