Hey I run a 605c and have for the last 3 years. Got a good deal on. Paid 500. I run it with a 33 hp mahindra. It handles it and can make a full size bale but I usually don't because there harder to handle. U dont need alot of hp to run it as its closed throat.
It does take some time to get good at starting a bale but once it's rolling your going to town. Check the belts for broken splices also check the front roller bearings as they are the hardest to get to and usually don't get redone. U can go online to Vermeer and get a free manual and parts book which is really nice for repairs. They were top of the line balers in thier day and are still very dependable.
Make sure the owner gives u a crash course in it operation as all balers can be very dangerous. Never go under a raised tailgate there's no lock on old balers . It will kill u dead.