Have this excellent extender for Canon EF lenses, that I've used a few times on my 135mm 2.8 and 300mm 2.8. Works great and doesn't deteriorate the image quality.
Further details here
https://www.canon.com.au/accessories...ender-2-0x-iii
Retails for $700, I can do $480 plus shipping.
Condition is like brand new, with no marks or scratches.
Can be picked up Inner West Sydney.