20hp is more than enough on a well engineered machine. I'm not familiar with the 3206. Is it a liquid cooled kawasaki? or a kohler command? Either is great. IIRC, The 3200 series typically has 2 spools of hydraulics, power steering, diff lock, etc.. A new 3200 series would run ~$6-7K new w/ a deck. A cpl hundred hours is nothing. If it's 4-6yrs old, I'd say it's worth around $3500+ for the tractor & mower deck. More if it includes other attachments.
Joel