I run ST4S plates in my slipper with no problems at all. They are about the £115 mark.
You can get Bucci for about £140 and the surflex ones, the most common carbon faced plates, for about £160.
Barnett plates are available from PDQ I think who distribute them in the UK. They are pretty pricey if I recall.
I'd go for the ST4S if moneys tight. I've got about 8k on mine and I do use the slipper a lot
