I think this is a great alternative for us "Do it your selfers".
Bearing in mind its a kit that you put together yourself I think you have to be very competitively priced compared to other units that are already commercially available and are already assembled with a warranty.
The one that springs to mind is the Rottendog units which are USD$185 ( + shipping ) for 5 x units. They do look good and also have the comma on the displays.
http://www.rottendog.us/DIS021.htmI think as they are a kit probably around $150 - $170 would be the go but I am fully aware that the cost of all the pcbs and other components in this kit will probably be quite high especially going on Jaycar prices.
I would say Rottendog probably source all their components out of China or Taiwan and who knows they probably have them assembled there too which brings down the cost quite a bit.
I think this is a great project and I dont want to be a "downer" but I think they need to be priced less than other commercially available units so you dont get stuck with a lot of stock that doesn't sell.
I think most of us here on the forum are quite interested but if you want to sell overseas as well our Aussie Dollar being so good might make that quite hard.
Chris
