Wow! There are a lot of different things running around in this thread and there may be a lot of confusion going on. A "3rd function" FEL kit is normally a electric diverter valve operated by a button on the joystick to give a third function to the normal lift and curl functions of the FEL. A "rear remote" kit can do the same thing if you run hoses all the way up to the loader and use the remote lever instead of a button on the joystick. This rear remote can also be used for any function on the 3PH by disconnecting hoses to the loader and attaching them to something on the 3PH like a hydraulic toplink. This is the kind of kit that holtzacres is talking about.
jjbath, is talking about a rear remote kit on a TC35 which is a whole different class of tractor from the TC30 the OP originally asked about. jjbath, if you check at Messicks.com, I think you will find the cost of the first rear remote kit for your tractor is about $550. You can add two more for a total of 3 remotes, and #2 and #3 are a little less than the first one. I haven't checked, but that is fairly close to the right price. If you don't know how to check, I'll try to assist you.
I believe this explaination by Gumby6 over on the New Holland site may help.