Default Slim Rom for custom devices

I am looking into buying unbranded tablets and phones to sell from my IT Company here in South Africa. If I decide on what products I want to import what will a ROM developer charge me to make 2 slim roms a year per device? Obviously with my company branding on the device itself and the rom developer must put my backgrounds etc.... on the rom. Any takers?
Htc Artemis
Unlocked