Renault Laguna Rti 2.0s 1997 ?

Its a intermitent problem cylinders 2/3 stop working,they work ok for a few days then stop or it happens alot in one day I know it sounds like the coil but it might be the E C U, but a new E c u will cost alot more than the car is worth or can I buy second hand.Can someone help its driving me nuts.