Exakta cameras are very peculiar contraptions, beautifully engineered, but difficult to use with left hand wind and shutter release. There might be some hard core followers who are still using the Exakta for general photography, but there are few.
Extension tube sets sell for around $20. The 135 mm lens ,if a coated pre-set or automatic model probably is in the $20-25 range. If manual or uncoated, even less. The 300mm, depending on the nature of the problem, could be worth nothing to a user. Any value would be to a collector who only wants to display, but not use.