The cost shouldn't be a big concern initially, but if every diode requires 1g of Pd then pretty soon we are talking real money here. Pd is used in electronic parts, but in micrograms. A catalytic converter from a car may cost about $1000, in part because it contains rare metals.
The article admits that chemical reactions are likely in the test device because H2 and D2 are producing the same voltage. Let's see what happens after they do more research.
Much of the research into LENR has moved on to Nickel, a far cheaper metal.