I did had monroe's on another car of mine.. there is a reason they are cheap. Alfaowner (http://www.alfaowner.com) do G&M kits which are cheap - don't know if they are any good though. Or Boge (made by Sach's, one of the OEM suppliers to Alfa), equaly cheap but I guess you get what you pay for to an extent.
I seriously doubt if Monroe, or Armstrong & Gabriel make any real efforts to valve their dampers correctly.
As fade2grey said, you get what you pay for. And the quality stuff lasts a lot longer. 140 000 km on Bilsteins is not unheard of. Never heard the cheaper brands last so long.
You missed out as Henry had a source in Germany a couple of months ago. They were £100 for a set of 4. Even came with the genuine alfa part no. stickers on the box. They lowered my super by about 30mm, so guess they lower the sport by 15mm. Don't think you can afford to go much lower than that anyway as the ground clearance isn't huge anyway. The best bit is the ride actually improves unlike most lowered springs.