Richard I have done a couple of 450Ds and would like to encourage you to have a crack at it yourself, it's not really hard to do and you'll learn alot about your camera in the process. There is a good online step by step guide with photos to help you through it. Check out Gary Honis' excellent tutorial here on the filter removal steps:
http://dslrmodifications.com/rebelmod450d1.html
There is a camera store in the Sydney CBD that will do the filter removal for you if you wish to pay a professional, but I can't remember their name - perhaps a search here will find it, or someone will chime in with the name. I think they were charging $150 to do it.
If you do decide to try it yourself, just be methodical, and follow Gary's steps precisely, and tape all the little screws onto a step # sheet of paper so that you don't loose anything. It helps to have a set of small phillips head screw drivers (jewelers type usually sold in a plastic case - they sell them at Bunnings), a small magnetic one is a good idea as well. You'll need some toothpicks to manipulate the ribbon cables (the hardest part of the job in my opinion). Draw a line across the ribbon cables at the connector before you removed them so that you know when they are properly in place on reassembly. When reassembling follow the steps in reverse. Its also a good idea to clean the sensor and both sides of the front anti-alysing filter is your leaving that in place.
Good luck.