interesting question. my simple solution:
cost of components + markup.
the cost of the components should be a stable item.
markup: you have r/d cost associated. you are still in this stage, so final r/d cost is unavailable.
profit: how much do you want to make per unit sold? 10%, 20%, 200%?

i would suggest get all of the bugs worked out, complete your r/d and produce some performance numbers.

AND

i would suggest using this forum as a test market AFTER you finalize ALL cost.
keep the final cost low, [but make your reasonable profit].

THEN

look ahead for the MB crowd as an additional marketplace to sell to with an 'in production', and proven product.