Canon Lens Cleaning (1 Viewer)

I have a Canon fit Sigma 400mm lens that needs cleaning inside, anybody know anybody who can do this at a reasonable price, I've gone to the big boys and told it would be £250 minimum, there must be somebody who does this from home for reasonable cost, the lens isn't worth near this, scopes and bins can be cleaned for about £100, anybody help?
Thanks

What type of dirt is in the lens, and how do you see it?

If it's dust, and only visible by shining a torch through the lens, most people would say the effect is minimal. So don't waste your money. OTOH if it's fungus, it's probably not worth bothering as the fungus attacks the finely polished lens surfaces, so a clean and an expensive re-polish (and re-coating) will be necessary. (Or replacement of the affected elements by Sigma.)

Your query does raise some points. I quite often see on commercial used lens websites that the phrase "lens contains some dust which won't affect images"... And I think to myself, has the shop used the presence of dust so as to seriously lower their trade-in offer?