I have ordered three 2x3 Pacemaker lens boards from Peter Wong at developstopfix https://www.etsy.com/shop/DevelopStopFix?ref=search_shop_redirect for $14.95 each and I'm totally pleased with them. Then today he told me he sells 4x5 Pacemaker boards at the same price.

This is a much better deal than anything I've seen on eBay. The only guy selling new lens boards there molds them out of plastic. They're a bit cheaper, but he warns they may need trimming or filing to make them fit. Peter's lens boards are aluminum and are a perfect drop-in fit.