My rear was rebuilt by K-Tech, £63.83+VAT.

Some people have a problem with K-Tech as they won't do something or try to sell you something unless they think it's the right thing for you, with the stock rear shock the "problem" is, rightly or wrongly K-Tech don't think the damping can cope with it and thus wont fit an uprated spring.
They'll also try and talk you away from buying a fancy shock unless you're properly quick.

Depends what you want really, in my experience, Maxton will do what you ask and take your money, K-Tech will ask what you're doing and advise on that based on their knowledge.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread