For pricing, it partly depends on where you live. It can also change from one year to another or from season to season within a year.
You can go to 
www.tractorsupply.com
Somewhere in the top left part of the screen, it will tell which store it thinks you are shopping at. You can change that to one near you (it always gives the wrong one for me.)
Then search for "layer pellets" and look at the prices it gives you.
I often see the cheapest non-organic layer pellets about $16 for 50 pounds ($0.32 per pound), with organic having higher prices and sometimes smaller bags (which usually goes with an even higher per-pound cost). Looking at the options will give you some idea of what the prices are in your area.
You can do similar searches on the website of Walmart (you can tell it you only want to see what is in-store in your area) or Chewy (they only ship, no local store, but shipping is typically free if you buy more than a certain amount at once.)
Is there a reason you want layer pellets? You could feed chick starter or all-flock feed to all of them, and put out a dish of oyster shell to provide more calcium for the layers. That is really the only special thing in layer feed, the extra calcium.
If you feed them all the same feed it makes your life simpler, especially if you have them sharing a coop at a point when some are laying and some are not.
If you feed them all one feed it generally means they eat fresher feed too, because they all eat the one bag instead of taking twice as long to eat two bags.
I have never tried it.
About cost, my personal decision has been that I am not willing to pay extra money for "organic" in human food or pet food.
Hopefully someone else will have more helpful thoughts on that matter.