That would explain the cost (that is a really slow pick and place). For comparison I designed a board a few years ago that was a 6" by 8", 4 layer PCB, parts on both sides, 163 parts, several orders of magnitude more complex than an Arduino. For 1,000 unit runs the the per unit costs were $2.97 for the PCB and assembly with flying probe test was $3.51, including post processing for several parts that were not reflowable, done in Asia by a contract manufacturer.