I haven't actually played a deck building game, but I've read a little about Dominion and I think that sort of option could potentially work with Fluxx. A few ideas off the top of my head...
As far as the starting deck, since everyone cannot have identical decks at the beginning of the game, maybe you could have a selection of themed decks each containing similar cards, but more focused in one area. Like one deck could start out with Draw 2 in their deck, while another starts with Draw 5 or something.
This being fluxx, though, the starting 10 card deck could be whittled down to 3, and you take off from there.
Perhaps keepers wouldn't start in anyone's deck, or goals cannot start in anyone's deck. Something like that.
As for a pricing action, you could have the current play rule govern how expensive the cards you can buy are. For example, if play 3 is out, and a card costs 2, you could buy that card by discarding 2 cards, then you'd have to play one other card. Play All would obviously give everyone a chance to buy any card(s) they want as long as it's out and playing the remainder of the cards from their hand, but you wind up with an empty hand.
Obviously this brings up the fact that if the play rule is lower than the price of certain cards, they cannot be bought. Not so! Make it so that players have to buy cards at the beginning of a turn or something, and they can buy any card that they want for any price as long as they have the cards to discard. If they've discarded more cards than the current play rule (ie bought a card for 2 or more with Play 2 out), then they just don't have any more plays that turn.
Just a few random ideas from a person who hasn't physically played any DBGs before. :)