Plusnet are currently offering 12 month contracts with unlimited standard broadband for £3.49 a month.
A good price in itself.
However if you add a line subscription and prepay for 12 months, then the line rental will cost £155.88
If you order via topcashback, then you can get £101 cashback this week.
After you have paid for the router P&P your total cost after cashback is just £106.24 for unlimited standard broadband for 12 months including line rental.
This works out to £8.85 per month.