Each BC laser can use up to a maximum of 4 mj/t. Any more than that will be wasted, as 4 mj/t will make anindividual laser run at full speed. Adding more lasers to the table will speed up the crafting process considerably, you just have to account for each one receiving a full 4 mj/t to make it as effective as possible.
So to answer your question, yes, adding more lasers costs more MJ, you just need to multiply the amount of lasers you have by 4 and provide that amount of power using whatever medium you choose (redstone energy conduits, conductive pipe, engine, tesseract etc...). For reference, say you had 20 lasers on 1 assembly table. Running all those at full speed would take 80 mj/t, which you could get any number of ways.
For me, easiest thing to do was to setup a wall / line of engines somewhere and feed that MJ into one or more tesseracts (which are easier to make and use than many might be led to believe). This would allow me to pull that MJ whenever needed either in the house, or in the open world, without the hassle / cost of wiring. In the above example of 20 lasers on 1 assembly table, I would set them up in this order:
1. Place assembly table + adjacent chest for output collection
2. Place walls at necessary distance (lasers have to be within 4 blocks of assembly table)
3. Place lasers so that they are facing the assembly table from any angle (just test to find your preference)
4. Wire lasers using redstone energy conduits connected to the back of each engine
5. Connect 1 energy tesseract set to RECEIVE (from the aforementioned remote wall of engines)
6. Place a lever nearby and wire it to the tesseract...This will alow you to turn off the power easily when done w/ the lasers.
While this setup is not really early game, the same could be accomplished with 1 laser + engine (preferably outputting 4mj/t) and a lever on the engine. If you go this route, I would recommend using either an electric engine connected to your power grid (upgraded to 4mj/t from the base 2mj/t), or a magmatic engine (4mj/t) using lava. Neither one of those will explode if you for whatever reason forget to turn them off, and although a combustion engine will output the necessary power as well, it's easy to lose your whole setup if the engine blows up from having nowhere to output it's power. To prevent those explosions you would need gates, but that's a whole different discussion...
And this is what happens when I get interrupted every few seconds...LONG POSTS >.> SORRY!
