In short, it's $1.99 an issue - $19.99 per year.
Seems reasonable. Magazines make their money from advertising, which is why print subscriptions run $10 a year (cheap). With digital, added features are possible (interactive stories, video, audio, links, etc) so if those features are fully utilized, I'd be willing to shell out $19.99 a year.
It's like buying a tv episode on iTunes versus a season pass.