UMIDIGI shows the cheapest bezel-less phone I have yet found, selling at only $90 in bulk to distributors who order at least 1000 units (if you are a distributor, you can contact them at the contact infos below to enquire about price based on your order quantity). UMIDIGI positionned the phone call speaker hole at the top of the phone (I am not sure if sound quality would be best, I was not able to test it) and the microphone is below the phone on the side. Only shipping HD 720p display for now, but they also plan to have a 6" version to be called the UMIDIGI Crystal Pro coming as soon as Sharp is providing them with the 6" display (that one would probably be 1080p).
Distributors can contact UMIDIGI here:
SHenzhen UMIDIGI Technology Co Ltd
Hugo Cui, Business Development Manager