The average cost of a full-time nursery place in Britain has reached �7,400 a year, according to the Daycare Trust (8 Feb 2006) with typical costs for a child under 2 being �142 per week, more if you are in London. As redcrx has said, you should make enquiries at local nurseries to see what the going rate is.
Your employer may also run a childcare voucher scheme, whereby voucher �amounts� deducted from your salary each month to be paid towards professional (registered) child minders. Although the allowance comes out of your monthly salary, I believe it has some tax benefits.
Sadly in many cases it becomes more beneficial financially (and psychologically � difficulty in balancing work & life etc) to not go back to working full time at all, maybe just part time with flexible working hours. This site might provide some useful advice:
http://www.netmums.com/cpg/whatmatters/greatwo rkdebate.htm