If I can provide the board in case cheaper than buying just the board from Amazon (which I can) then, why not?
You might want to do do some business calculations.
What is your time worth is the first basic one. Then add up all the ancillary activity costs of making it happen, distribution, packaging, cost of scrap faulty lost in post, customer support time, warranty and product failure, marketing. Business income tax, cost of inventory sitting around waiting to be sold, cost of payment services (credit card PayPal) etc etc. What margin is there and how many do you need to sell. Then how much profit do you need to make on top of that to make it worth happening.
Don't let that put you off or think this is intended as me discouraging you, There is a market for a DIY low cost option, not sure of its size, but its there.
Just saying be absolutely thorough in calculating your
true costs and
time and
effort and what your objectives are at the end of the day, for what you want, or need to get out of it.
It really, really isn't just the cost of components as some seem to think.
I hope all that doesn't sound patronising, sorry if you have already done all that and the numbers stack up for you.