I was lucky enough that some of the strip were cut from scrape pieces. So wasn't charged much for those. I bought a sheet of plexiglass ( I believe its 1/16" thick) 36x24 and had them cut the stips from that all my strips are 24" long. I started with the sizes I use most, then every couple of weeks got the other sizes I needed. Tried to get as many as you can from scrapes they have.
I wrote on each strip what size it is so I know at a glance. I also made a whole in each so they could be hung up
I went on paint and made a crude example of a strip with the square marking