Erm, IIRC the Eibachs are about £165 and the PI were about £115, but I got the PI's off ebay for cheeeeeep man lol!! Thats really why I went with them tbh, was gona go 4 Eibach, but to me they'll pretty much do the same job.
The front 2 just kinda clunked as if they were jumping.. took them back and they took them off, re-fitted them and greased them up, since then its been fine really!!
Just go for either 1 mate, I bet you wont even be able to tell much difference, I'll probs get slated for saying that but have a go at either 1 and tell me if you feel any different lol
iirc, the back sits higher on the mera anyways, so if allround is lowered by the same amount, the car will still be lower at the front. Its better I think anyways, more stable and better for cornering if the front gets down better..