It's listed at $7.00 plus shipping - it's a UCLp 56.8mm x 2.25mm. I ordered two and it came to $16.50 total.
Here: http://www.flashlightlens.com/index.php?app=ecom&ns=prodshow&ref=UCLp_AR, then choose the size from the pull-down. Yes, they are rather pricey. I'm thinking what RIC has going on here: https://budgetlightforum.com/t/-/27826 sounds interesting for the Y3 as well. His AR lens in the past performed decently in independent tests, not as well as UCLp's but close (https://budgetlightforum.com/t/-/20748, https://budgetlightforum.com/t/-/19458) and they will certainly be cheaper, free shipping, Int'l shipping, etc. Problem is his stating the min qty of 50, so without someone organizing it, I don't see how this will work out.