: even if you try to get this achievement in the cheapest way possible, it's still going to be pretty costly. Assuming no separate track packs, exports of RB1, 2, Lego and Green Day, all free DLC and 26 cheap RBN songs to top it out, you're looking at 4880 MSP before counting the costs of the exported games themselves.
For those with smaller hard drives, it has been confirmed that you do NOT need all 300 songs on your hard drive at one time if you're concerned about space.
The most cost efficient way to add to your song count is through exports of other games. At the bottom of the solution is the number of songs that can be exported between games. If you need to buy another game in order to export the DLC, make a note to buy new! With the exception of Rock Band 1, which doesn't matter if you bought it new or used, used games likely will not have the export code available. Also note that The Beatles: Rock Band will not export at all.
Rock Band Blitz - 25 songs
Rock Band 1 - 55 songs, 400 points for export
Rock Band 2 - 70 songs, 800 points for export
**Free DLC Pack - 20 songs, requires RB2 manual code
Lego Rock Band - 45 songs, 800 points for export
Rock Band: Green Day - 44 songs, 800 points for export
Free DLC (Rock Band Free 1 pack, Still Alive, Promised Land, Charlene (I'm Right Behind You), Headphones On, Dreaming of Love, Am I Crazy) - 15 songs
274 165 songs overall
From Groudon199 and Llamaman2, the RB2 free songs, Lego Rock Band and Green Day exports have now expired. If you did not already have them, you'll have more to make up by DLC.
For the last
135, there are essentially three options:
1) Track Packs offer 18-21 DLC songs with no additional export cost.
2) DLC Albums. While this is the most expensive option by far, if you did not export Rock Band: Green Day, it will be necessary for the Loyal Fan achievement.
3) Rock Band Network has several songs listed at 80 points to top off the collection.
Whichever way you slice it, consider saving 160 points for a Johnny Cash song, as six of his songs are currently the only ones counting as a '50s decade for a separate achievement.
From xs Silence sx, if you're the social media type, there is a Rock Band World app on Facebook that will tell you how many unique songs you've played amidst other data.