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They actually costed me a bit to build (I built ten of them), about 90€. The 5L bucket with lid is something like 4€ each, the bait (bananas, sugar, wine, beer, year, syrup, apple) was something like 20€ in total. I made the entrance funnels by cutting out pieces of suitable shape from stiff transparent plastic that where supposed to be used for having under your plate at the dinner table! I needed two of those plastic sheets - 4€. I folded the cut-out plastic pieces into tapering tubes and "sewed" them together with steel wire (this was the toughest and, admittedly, least elegant, part). At first I attached the funnels to the buckets with silicone gel, but this was not very effective and I realized that since the funnels themselves tend to expand, I could simply attach them by putting strips of elastic window isolation bands between it and the bucket: