Copy-paste from link above (in case it's blocked at your workplace)
Sad to say that the downloadable songs for the Guitar Hero, DJ Hero and Band Hero games, and the Guitar Hero mobile game will no longer be available after March 31, 2014. The Guitar Hero servers will stay online and any previously purchased downloadable content is unaffected by this change.
We want to thank all of you for supporting Guitar Hero over the last nine years. To celebrate this great community, selected songs and tracks will be available for as much as a 50% discount on Xbox 360, PlayStation 3, and Wii from now until the end of the month.
For more information, please visit the store on your console.Also, over at the iTunes store, the mobile game will also be available at a special discount until the end of the month.
The Guitar Hero songs are $1.35 AUD (bar a few).
and DJ Hero packs are $3.95 AUD (can't buy separate tracks).
However, everything is cheaper in the US. If you have a US account (360 or PS3), Guitar Hero songs will only cost you $0.99 USD and DJ Hero Packs are $2.99 USD.
Damn, that is a pity. Thanks for letting us know OP.
I am now learning to play a real electric guitar because of this game but I'll definitely have another look.
Regards
Daniel