Fares of AC locals should atleast be at par with the current Non-AC first class fares. Passengers paying a hefty fare for First class don't actually get any perks apart from cushioned seats and tinted windows. During peak hours, the FC coaches are as crowded as the second class ones and very few people actually get to sit on those *cushioned* seats.
So, reducing AC fares and making it at part with FC fares will benefit a lot of FC passengers. Further, many passengers currently travelling in Second class may migrate to AC since by paying some extra amount, they are actually getting a tangible advantage/benefit over the regular Second class which they weren't getting by migrating to FC.