It used to be ridiculous. It's now downgraded to merely comical. I'd check out the link above, but my understanding is that you don't have to pay to publish an app. You might be referring to just publishing strictly to the newstand, though. In that case there are both "multi-folio" and "single-folio" options.

I think the bigger issue, besides pricing, is content lock-in, as you note. I've seen some other systems (not Baker, I'll check that out) that offer "free" app wrappers for magazine style content but tightly control the creation process as a lock in mechanism (and I'm not even referring to Apple here).

Curious: are you actually publishing to newsstand or standard apps? I'm wondering what the barrier to entry to the newsstand is in terms of approval vs. apps. At least with ebooks, it gets weird quickly on Apple's end (long long approval times for independent publishers unless you go through an "approved" broker, etc.).