I found something similar when I went to buy a BMX for my son's birthday earlier this year; despite asking the sales assistant and double-checking the price, it had gone up 20 quid by the time I got to the till!
The floor manager was downright unhelpful and initially completely unwilling to compromise in any way; in the end I paid a tenner more for it - had we not been leaving on holiday that day and only returning on my son's birthday I'd have left it there and bought somewhere else (we're kind of short of LBS in these parts, and I doubt I'd have found anything similar in stock elsewhere in town.)
In the end, thanks to quidco cashback I didn't pay too much more than the sticker price but it still annoyed me greatly and I certainly won't be buying another bike there.
Oh yes... when I got home and checked online, the online price was still the original one as on the price sticker in the shop.