I have a Sony KP-57WS500 57 in. Rear Projection Television with the color red tube not working i want ot know how much 4 a new one and how hard it it is ti change.

Sony does not make the tube available. They want you to remove the Red CRT with the Optic coupler and send it to them so they can remount a new CRT to the old Optic Coupler and they will send it back to you. This usually cost $300.00 to $400.00. It is a major tear down to remove the CRT and there will also ba a alignment of the convergence after the CRT is reinstalled. If you are really interested in doing this, let me know and I will do my best to give you instructions. Something else to consider is that the other 2 CRT's will likely need replacing soon. It is a lot of money to put into a older set that Sony is not supporting anymore. When you add up the parts cost alone for all three it is $900.00 to $1200.00. With the prices of LCD panels coming down in price you could replace the set for the cost of the parts alone.
I hope this helps,
Skyassoc