The title is not a mistake, this bundle genuinely does start at $0. My guess is it's a way of saying they're giving away the lowest tier for free, the cost is your effort in signing up to the web site. Don't forget that Groupees allows you donate a portion of your spend to charity!
Anyway, Shirobon began by creating chiptunes on a GameBoy, which is largely what the two 'free' albums are on the first tier. He's progressed over the years to more sophisticated electronic sounds using other instruments, but still with some chiptune influences. Even if it's not your main cup-of-tea it's actually an interesting journey just to hear how his sound has evolved. At US$5 for the first three tiers it's cheap enough to at least give it one listen through.
For US$0 (~AU$0 - duh!) Minimum You Get:
Connected - GameBoy Chiptunes
Golden Apples [Remastered] - GameBoy Chiptunes
For US$2 (~AU$2.60) Minimum You Also Get:
22:22 - "Experimenting with sounds away from the consoles"
Back Tracking - Chiptunes on GameBoy and C64 blended with futuristic sounds
Dimensions - A combination of GameBoy chiptunes and modern sounds
Pleasure Island - FM instruments with Funk/Pop elements
For US$5 (~AU$6.50) Minimum You Also Get:
Regain Control - The Remixes - Single release of ‘Regain Control’ with a few remixes from other artists
The Arcade Dream - Modern instruments with chiptune elements
Pleasure Island (The Remixes) - Album of the same name remixed by other artists
Shirobon - Infinity - Chiptunes ahoy!
Distant Reality - "Blending together the sounds of Chiptune, Modular Synthesizers, Drum Machines and more"
For US$10 (~AU$13.01) Minimum You Also Get:
Shirobon Presents: Chiptune For Serum - Want to make your own chiptunes? Shirobon has put together a pack of sounds, demos, and presets for you to use in Serum, an 'Advanced Wavetable Synthesizer'.
Bonus Section:
Compose a song without being able to hear it! - Unlocked at $2000 (currently at $1311)
This is a bit weird so I'll let Shirobon explain it himself: "I will put myself in the shoes of a person who has lost their hearing but still has a passion to create music. I will do this by creating a song from start to finish without ever being able to hear what I’m working on. The speakers will be off and I will only use my eyes and best guesses at creating a song and won’t ever hear it until it has been uploaded!"