For any that might be interested, MLB's Audio package is supposed to be released tomorrow. For the past few months, all links relating to Gameday Audio have led to the TV packages, which implied one could only get it along with the $100+ TV packages.
Anyway, crack MLB staff seem to be confirming that a Gameday Audio package will be available "tomorrow" (which they apparently posted yesterday). Some teams (Yankees, Mets, Cubs, Indians) seem to have some kind of fan club that includes Gameday Audio, but I haven't checked to see if any of those are any cheaper.
I'm dumping Extra Innings this year (which is $200 for those of you interested)... I'm still considering MLB TV instead but less now that audio-only packs will be available. I remember a lot of complaints about the MLB.TV feeds last year, so I'm curious if any are letting their subscriptions to it lapse.