Food for thoughts:
I think the best way to go on balancing most ADCs would be to :
1. Tune their kit around these 3 main stats: critical strikes, lifesteal and attack speed.
2. Change item itemization to only having AD + one of those stats as base stats. Most AP items hace AP + one other offensive stat if I remember correctly (mana being a ressource).
For example, Statikk Shiv could be the AD/Attack speed item and RFC could be the AD/Crit.
Like I said, food for thoughts.
Edit: I forgot Phd. It could then be an AD/lifesteal item. My original thoughts were that Phd/Shiv/RFC would be the cheap ADC items at around 2700-2800g and ER/IE/BT would be the expensives ones at 3100-3400g.