Same deal as they are running on TV
Just run a test order and get
Unlimited broadband (First month)£9.99
Promotional discount (for 12 months) - £7.50
Plusnet Protect powered by McAfee (First month)Included
Line rental (First month)£15.95
Weekends (First Month)Included
Voicemail (1571) (First month)Included
You get the higher price because you appear to be not in the large low cost area and taken from the legal bit on the landing page
Unlimited broadband from £2.49 a month for the first 12 months then £9.99 a month when you take line rental - 12 month contract:
•Receive a £7.50 discount each month for 12 months on the standard Unlimited Broadband price of £9.99 a month (or the standard Unlimited Broadband price of £17.49 a month if you live outside of a low-cost area).
It is only possible to check if in the low cost area once postcode/line details have been entered. So you still get the £7.50 a month discount, just the starting price is higher.