I want to build a couple around the house with scrap wood to see if they help with the mosquitoes that the hens can't get
Have you tried asking friends or family to save them for you? Once in awhile I post it on FB & tend to get enough for months to use. The people who buy them from me also return them.
Friends used to save them but since DW has been sick and we've not been in church I don't get any. I do have some customers but they don't always save me enough. I toss any that don't look clean to me.
I prefer styro since they can be washed out.