I like this idea, maybe something like this...
Demonic Bargain
Enchantment
~ enters the the battlefield with X credit counters.
Pay X life and remove a credit counter: Draw X cards.
When there are no credit counters on ~, sacrifice ~ and put a 5/5 flying Black demon creature token into play under each opponent's control.
Another idea
Intense Hatred
Enchantment
Pay X life: Target creature gets +X/+0 until end of turn. At end of turn, sacrifice that creature.
(It's channel/fireball all over again!)
The first one would be so, so broken. Play it for X=2, then pay as much life as you want to raw lots of cards and keep the card around with a single counter on it for the rest of the game. If it required that you removed X credit counters from it, everyone would end up playing it like "X1[base cost]: Draw X cards and lose X life.", since they'll just choose not to remove the last counter to make sure the demon doesn't come out.
That's why I suggested adding debt counters and asking for a payment for each of them per turn, since removing them as a cost means players will opt for removing counters until only one remains, and then doing nothing. Ticking counters down per upkeep works a lot better if you want to remove them rather than add them, but in that case it's either the broken or bad offspring of Phyrexian Arena and Yawgmoth's Bargain.
The problem with the second card is it makes you pay the mana cost once, and after that you get a repeatable instant-speed Hatred that only costs life, so its mana cost would probably have way too high to keep it from breaking constructed decks in half. Even if you lose the creature at end of turn, most players will just pump enough life into it to kill their opponents in one swing; very few will make the mistake of only pumping their creatures a little bit (unless the environment is full of powerful instant-speed removal or they want to sacrifice their creatures, that is).
Here's another idea:
Reprocessing Plant 1BB
Enchantment
Sacrifice a creature: Put a material counter on Reprocessing Plant.
1BB, remove a material counter from Reprocessing Plant: Choose one - Draw a card; or target player discards two cards; or target creature gets -3/-3 until end of turn.
It's an engine card if there ever was one, and I'm not sure the effects are balanced with one another. I tweaked the cost and effects a bit, and I find it funny that the effects ended up being 1, 2, 3 (draw, discard and minus effect).