Frozenbyte mentioned on the Steam forums that they're not that happy about the pricing either and there are some bureaucratic bullshit going on (not in such colourful words but that feels like the general idea.)

But I prepurchased anyway, even without online co-op since it comes with Shadowgrounds, which upon playing I enjoy very much.

So Shadowgrounds + Trine feels like a good $30 ($38AUD) combo.

If you haven't got Shadowgrounds, it's quite a good deal.