I was wondering the same thing last month when it was still summer

I found a guy on Ebay who was breaking an SL who wants around £500 for the complete kit.

If you can't fit it yourself you're looking at £250 - £500 to have someone else do it.

I solved my problem by buying an SL with aircon 2 weeks ago, unfortunately it has only been needed once since

All this is useless information for you if you're not in the UK though