The JD 447 is a good simple 4 foot by 4 foot baler. They are twine tie only and have few fancy things on them. That makes them a very good baler for the smaller hay farmer.
Your Kubota M5030 should handle it fine unless you are on real steep ground. You did not say what they wanted for the baler. If it looks real good then they will usually bring in the $7500-10,000 range. There is a pretty good demand for them as not many where sold new. Lots of smaller hay farmers are looking for a simple baler.