Asking around my office, the cost for a coped-web side plate connection is around 50% more than the same connection uncoped. Like apsix mentioned, the main additional cost is from cutting the steel to cope the flanges.
I would expect the total cost of the connection to be in the region $AU200-300 (better ask your steel fabricator, I am taking this value from a decade ago, making adjustments for inflation plus the increase in steel price and the ever increasing labour cost over the same period). A Quantity Surveyor will probably be able to give you an answer as well.
I have found in my designs that despite a coped web side plate being more efficient in terms of reducing the beam reaction eccentricity, the connection is generally not critical. I keep my designs pretty standard, M20 bolts, 3 bolts for 300UB's, 4 bolts for 400UB's etc. 10 plate cleat and 6mm CFW. The critical aspect of the design is the weld shear that will increase will the greater eccentricity, but generally I have some capacity up my sleeve.
I wouldn't expect the savings in cost to be astronomical, and there are probably better ways to make the steel detailing more cost efficient.