Depends on the lights you use and how efficiently you are using them. I use a simple kitchen light led system mounted under the kitchen cabinet to grow some herbs. 450 lumen, nothing fancy, just ordinary white kitchen leds. The system is rated at 14 W. So that's 0.014 kwh. It's on for about two thirds of a day. So, a month of running this would cost me about 7 kwh/month. Depending where you live that's about a 1-2$ in electricity cost per month. Low enough that I did not actually look up my KWH price so can't tell you down to the cent. But cheap enough and I like having fresh herbs around.

I've been running this over a month now. It's mainly a proof of concept before I invest in some proper led grow lights next winter. Works great so far, my basil plants are doing fine and will move to the balcony when the temperatures rise a bit. There's enough room to have two or three small plants below the lights. Two healthy basil plants translate into an enormous amount of pesto if you treat them well. I must have harvested several kilos last year by the end of the summer. That's starting with two anemic supermarket plants.

This improvised kratky system probably uses a bit more. I would say it's probably 10x or worse. I've seen some fluorescent systems similar to what the lady in the video uses starting at 140W. But you can get bigger lights. LEDs are probably more efficient for the same amount of lumen.

From what I've read, lettuce is pretty happy living in shade with only a small amount of direct sunlight every day. I imagine you'd be fine to grow in a window and use no power at all.