CO alarm prototype and electronics design

I am developing a Carbon Monoxide alarm with a led screen which shows information (text) and acts as a clock when on standby. I need someone to design the electronics and make sure it works. Design the electronics, make sure it will work, design PCB and program the chip. The alarm is to have a LED light which is to be powered by a built-in rechargeable cell and last about 500+hours on one charge. This light will work independently from the main alarm ( as a bed side light). The CO sensor would be powered by a 9V standard battery, all other function would work from the cell. The devise is to monitor the power internally and show on the screen if it needed to be recharged. When the CO sensor goes of the light is to flash and the alarm sound as standard. It needs to be designed to work for the UK market. At the end of the project I want everything ready to hand to a manufacturer to get on with main production. I need to make the product as cheaply as possible so when looking for parts this must be kept in mind.