Also lifetime maintenance....

Bikes cause hardly any damage vs cars making potholes every year

Way more. I'm working on a road project now. Asphalt for a road (100mm thick) is being bid at approximately $35/sq.m. Granular are about an extra $30/sq.m.

For a standard residential size road (8.5m curb to curb) that puts you at $552/m of road length, or 33mil. The big costs on top of that number always come when you've got to remove the old asphalt and gravel ($75/cu.m), as well as all the fiddly little stuff like line painting, tying in grades to make sure you have drainage, sod restoration, tree plantings, etc.

$1-3m / km. So 60 km of 2 lane road would cost $60-180 million. Probably on the higher end for Montréal being an urban area.

But roads can cost as over $5Bn for 1.7km (looking at you Gardener Expressway). So $2,941 million /km for however many lanes that is.

These bike lane in particular are probably more expensive than brand new lanes, as they also require road adjustments.