It's always good to ask a question :) -- if you have one.

I would guess $25 in materials (at plumber markup).

Cap the drain pipe at the wall, cut off the supply lines near the floor and cap them, total materials cost of two cpvc caps is 44¢ and one pvc cap is $1.67. Then you need a slightly longer drain pipe and supply lines to get to the center of your vanity. I would leave a couple of inches of the supply lines just in case you want to change your mind years down the road.

We're having the plumber out tomorrow to do exactly that.

What about your lighting? You'll either want side sconces or a centered light fixture.

Your electrical boxes are too high and too close together for sconces.

I am very far from a designer, but I would do something like this

https://www.perigold.com/lighting/pdp/tech-lighting-ensu-led-armed-sconce-tlg4606.html

If you center the sink then it doesn't wind up as a space for 2 people to get ready... you may want to keep the off center sink...you can still do 2 mirrors ( or one large one ) and lights etc....

Good luck!

Our plumbing cost was $420 to change from two sinks to one. An additional sink, faucet, and sink cutout by the fabricator would have been at least that if we had replaced our original two-sink vanity with the same setup.

The offset single sink option is cheaper as you'd only have to cap off the second drain and water. You could do a double light over the sink and the counter so there'd be no need to change your electrical boxes. I considered the offset option and have several photos in my Vanity and Mirrors Ideabook.