Don't know for that one but cheapest on Digikey is $1.38 at 2500 off.
My guess is < $1 with negotiation for 10k (ie about £0.66) a lot less for 100k.
Be very careful with the MagJack pinout. There are several different pinouts, and RasPi has an unusual one. Check the RasPi schematics, PCB layout, and SMSC LAN9512 data sheet.