I think there is a bit of a misunderstanding. the $49 pack may give you RealTracks you might get next year as past of the standard upgrade. i'm not sure but i do know that Xtra styles are just that - complete styles you won't get without buying the disc.

for example Xpro discs are new styles using RTs available in the very basic pack. the cost of an extra styles disc is to give you new styles not new RTs.

and althought the $49 pak may include RTs you get next year, it contains 60 Unreleased RealTracks, 14 MIDI SuperTracks, 30 Artist Performance Songs with Vocals, 30 MIDI Styles, 12 Instrumental Studies, 20 RealDrums Stems, and a RealCombos Booster PAK with 38 brand new RealStyles, and more

so i really don't think you are getting charged twice for the same stuff