Colourless Mana Generation (not a card)

[Ephraim]

Is there a fair cost for the generation of small amounts of colourless mana?

For example, Sol Ring demonstrates that is far too small a price for a permanent that generates . Free for is right out, even with a land drop, unless the card also has some drawback or restriction.

I think that Thran Dynamo has a fair, but not game breaking price. is a fair cost for a permanent that generates . Sisay's Ring demonstrates that is far too high a price for a permanent that generates .

What would be a fair, but playable price for a permanent that generates . Could it cost ? Likewise, what is a fair price for a permanent that generates ? I think that the moxen demonstrate that even for colourless mana, would be too low of a price. I'm of the opinion that would be too high, unless the artifact also has some additional benefit, perhaps mana-fixing, such as ,{T}: (coloured mana) - such a card would be the artifact equivalent of the Henge of Ramos. Is a fair price to regain a land drop? Or it could ,Sac: (coloured mana). Is that too good?

[Matt]

[card]Worn Powerstone[/card]

If that didn't CIPT, it would be decent. At two mana CIPT, it would also be strong - making your curve 1,2,5.  At two mana and not CIPT, it would be an automatic four-of in every deck that can use , and thus too strong to be printed.

Half Sol Ring

Artifact
T: Add to your mana pool.

That would be EXTREMELY good. Broken, even, since you can chain them together. If it CIPT then it would be roughly as good as Llanowar Elf, which has been in lots of winning decks (just not in T1). Not CIPT makes it VERY VERY good, and probably a four-of in every deck that could make use of colorless mana.