I know when I bought my P's back in February of this year, it was about £50 for the P's (brand new) and the Star Circus pierce (brand new). Since then I've spent about £50 on a second hand P's (which came with the guide book, the Royal Change! pierce and a couple of other bits; all second hand, no packaging) and £40 (again, second hand, no packaging, also with a second hand Royal Change! pierce). I think it depends on if you want a brand new one or not, as I think they've gone up in price since I bought my first one, and whether or not you want any extras (usually pierces) with it or not.
I bought all three of mine off of eBay, although there's a traders group on Facebook that I've had no issues with buying from.
Hope this helps! ^_^