Sigma 105mm repair in UK?

[Bios.]

The autofocus in my sigma 105mm macro has broken, it just makes a high pitched whine.

It wouldn't normally be a problem as I never use AF for macro work however I'm going to the rainforest soon and will probably leave the 105mm on most of the time so would like to be able to use AF if the situation calls for it.

From what I have found out getting it repaired by sigma will probably cost £30-£40 and I was just wondering if anyone knows of places in the UK that might do it for cheaper?

I had a look through the repair thread at the top and searched a bit but couldn't find much.

Thanks.