Welcome to TBN.
To answer your question, go to Tractorhouse.com. Enter "Kioti" as the brand, and then enter the model you are interested in. I think you can also enter keywords (like "backhoe"). You will see a lot of examples of going prices for used tractors matching the criteria you have entered. Note: These are sample prices from many places across the country, and on TBN, everyone acknowledges that prices vary a LOT based on where you are located.
You should be able to find plenty of samples for both the kioti CK35 and the bobcat CT235 (same tractor). If you can't find one with the hoe option, I'd suggest an approximate additional value of 5500 to 6500 dollars (used as you indicated) for the backhoe. They are over $7000 new I believe.
-Mitch