Gah! So this exiles my permanent and will charge me - extra to recast it? For one mana?

It's a Swords to Ploughshares variant; giving you the chance to recast, instead of giving you the life :)

Also, hey, can this now be templated: "Exile target permanent until its owner pays "?

No, because they also have to pay the (say) to recast Elvish Piper in addition to the .

X should probably be something less difficult to achieve, admittedly. Life total was just the first thing that came to mind.

Also, Vitenka is correct. It is a Swords to Plowshares variant, because I am fond of those. I specifically tried to make one that Alex would be okay with.

Yeah, I don't think StP is allowed these days, even one with a tantalising get-out clause. At least not at this casting cost. Maybe at Desert Twister cost?

Well. Wizards is... somewhat conflicted on this. Basically, they print three variations on white exile-target-creature effects. One category is those that can come back later, like Journey to Nowhere or Banisher Priest. Those are fine in the colour pie because white gets temporary removal; they work like Pacifism.

The second category are at common, very expensive, removal for limited. These include Angelic Edict, Iona's Judgment, Trostani's Judgment. They're a bit annoying colour-pie-wise but they make a lot of sense for limited.

The third category is meant for constructed. They're one-mana instants as a nod to Swords to Plowshares. The most notorious is Path to Exile. They're pie-breaking and annoying.

I guess this card is an attempt to make something in the third category that looks like it's in the first category. Or perhaps vice versa. To me, my impression is the cost is way too steep to be practical, so it feels just as overpowered at StP or PtE.

Wait, hang on, Path to Exile is a real actual card? It's flat out better than swords! What were they smoking? Is there an article on that somewhere?

It's much worse than Swords on turn 1-2, because you're giving the opponent a free Time Walk. But it is still ludicrously good, yes.

FWIW, Mark Rosewater has gone on record as stating that he doesn't like Path to Exile, for example over here. That's more for a colour-pie-breakage reason than a power-level reason. People always knew it was going to be good though.

True, but what the heck kind of one-drop threat would you waste a swords on?

­Deathrite Shaman, perhaps.
I have considered setting X to either the number of creatures or the number of lands you control.

BTW, does "cast by paying X" mean "in addition to its mana cost" or "instead of paying its mana cost"?

­Goblin Guide, maybe. Garruk's Companion if you know all your blockers are 1/2s and 1/3s.

Oh, heck, toss an StP at a Tundra Wolves. The real question is "If your deck has enough removal, what wouldn't you throw a Swords to Plowshares at?"

why is path and swords break pie? what other color has they appeared in? what color should they be?

Alex, and many others, believe that removal for no "cause" does not belong in White's slice of the color pie. Note that this is an argument that springs from the more philosophical side of the color pie, which says that White should only get removal like Oblivion Ring, Banisher Priest, and Smite. O-Ring deals with things temporarily: there is an "out." Smite requires that White be attacked and represents White protecting itself or seeking vengeance.
Alex, and Maro, think that white shouldn't get unconditional, permanent removal, even though it gets just that in practically every set. They believe that Iona's Judgment and Trostani's Judgment don't belong in white. Personally, I'm on the fence.

You can see some discussion of the issue on this rather long thread. Most people on that thread agree that the unconditional exile spells shouldn't be printed even if they're expensive.

Here's MaRo's comment on why they still get printed.