Its 4 bucks a month for the transponder fee.... I still have mine though I hardly use the 407. Every couple months I toss $20 onto my account. I spend more in coffee in a week.... And its worth the elimination of a traffic headache on those days when I take it.
I chose to go by annual lease which at $21.50 annually cuts the monthly cost of the transponder to $1.79 per month. I don't use the 407 often, but the annual transponder lease is pretty cheap. If you do more than 3 one-way trips a year at the current rates for non-transponder monthly account fee and video toll charges, the annual transponder lease will save you money.