All that cost savings goes out the window the first time you get sued ;)
But also keep in mind that test fingers are used for more than just seeing if it can poke through a screen.
Way way way back when I worked in the auto supplier industry, we needed to test to make sure the auto-up windows and auto-closing minivan doors would actually not cut your finger/hand/leg off. We always used pencils as a first try. They break a lot easier than a dowel rod of the same diameter. If we were happy with the results, we'd get out the test finger. If it looked a little iffy, we'd suggest that the engineers should use their own fingers if they were really confident in their work.
Very likely they just wanted or needed certification-level accuracy. A wooden dowel would be very inaccurate for a bunch of reasons, including that its dimensions will change with humidity.
Test fingers and the like are very expensive because of the serious precision they have to be machined to, and are made of expensive materials to minimize dimensional changes the result from environmental variations and use.
Why was the "test finger" so expensive? What was it made of?
Why not just use a $3 wooden dowel rod from Home Depot?