I'd bet that electric window regulators probably weigh less than the OE crank type.

When I was working at a dealership, I used to replace window regulators all the time. The mechanisms themselves are mostly plastic and thin cable with a little motor. Some of the more recent ones are like a full door panel but the previous iterations were pretty simple.

There are general 'street rod' electric window kits a available. Not sure how you'd retrofit something like that into our cars though, probably more work than it's worth.