Probably all depends on a few factors Dan
1 how low do you want / need to go
2 how deep are your pockets
3 are you any good with spanners etc
I had mine lowered nearly ten years ago and then it cost me £2.5 k , prices have gone up a lot since then so the same job would cost more obviously
If you are good with tools your best bet would be to buy the parts and do it yourself, the nearest place that do a lowering service are type 2 detectives in Cambridge but I imagine that may cost three grand , depending on what you want doing
Hope this helps a little