Each Free Spin you receive is worth a £0.01 coin size, on the maximum number of lines on Rainbow Riches (20). So 20p overall.
Due to the Bingo rooms having different ticket prices it depends on what game you pick to play. The maximum value of each ticket is £1, if you use all 50 tickets on games that cost £1 then the value is £50. If you play on 1p tickets, then the value will be 50p.