The refund one would get will depend on the marginal tax rate of that person. But it is not a simple answer as the marginal tax rate will go down when your income less. Therefore you may get less refund.
Here is a calculator by Ernest & Young that can calculate the RRSP refund (please note this is an approximate number).
If you need actual number you need to do the tax return for both scenarios (without RRSP contribution and with RRSP contribution)
Please note the deadline for RRSP contribution for 2012 is March 1st 2013.