Bob,
What can you live with?
The cost of material (blank, & kit) plus time to make it, plus the selling location or market (the venue.)
So some of us use the 3 time our cost as a general formula to arrive at a baseline to price our work.
Your display, really made this picture POP, so little things like that can boost the price, even though you would not be selling the display with it.
Hope my 2 cents(USD) helps.