From the BTWholesale WBC price spreadsheet, 18/2 FTTC is £9.75 per month (ADSL2+ is £5.88 and 40/2 FTTC is £13 per month).
Openreach has a special offer price for 18/2 FTTC of £48/year for the eligible <10Mb ADSL lines on the selected cabinets.
(all ex. VAT)
How any of those prices will translate into prices the end user pays their ISP, who knows.