For pricing, I'm going to offer Ascension as a comparison.
It's a bad comparison for a number of gameplay reasons, including complexity per expansion (higher for Dominion) and apparent content per expansion (lower for Dominion). But the fact that it's a bad comparison doesn't matter for the sorts of people MF is (presumably and apparently) trying to cater to--casual players.
The online-conversion comparison is pretty good though, if we ignore gameplay. Currently, Dominion is available only on Win/OSX/Linux, and Ascension is only available on iOS/Android; both allow for cross-platform play. The Ascension implementation is a bit more polished than current Goko v1 without Salvager. More extensive comparisons are difficult, but I think that's a good summary.
Like Dominion, the Ascension base game is available for free.
Ascension has six expansions which cost $2 (one early small expansion), $3 (most of them) and $4 (one large expansion), and four promos (multiple cards each) for $1 each.
Dominion has eight expansions which cost--well, I can't see the cost since I've already purchased them, but I'm assuming from the $90 "total" cost that they're $6 (small), $12 (standard), and $18 (DA and likely Adventures), with six promos (one card) for $2 each.
Even ignoring the fact that I have to do math to convert dollars to ducats to expansions, as a casual player, there's not even a choice there.
$6 for an expansion of 13 cards (Alchemy) is trying to compete with $2 for an expansion of 30 cards (RotF). DA at $18 has 35 cards, and is competing with Ascension's RoV at $4 for 45 cards.
"But," you say, "any given group of 5 Dominion cards has more complexity than 25 Ascension cards!" Very good, you've identified yourself as a non-casual player, and you are not the main market.
LF hit it on the head: Making Fun's new prices are divorced from reality.
Now... this isn't really my problem, on some level. But if MF wants to succeed, increasing prices is not the place to start.