Reminiscent of Extraplanar Lens, but only applies to one land. Seems fine - it's pretty similar to ": Untap target land".

Almost - imprinting a City of Brass or similar lets you get round the downside part. But even then it's not horribly excessive, I think.

Aww, it's a lot less enticing now.

Hmm... so you're spending 1 from another land and giving up the 1 the land could have made, and getting 2 mana. So this artifact isn't adding any mana, just changing colours, which means is the right cost; see also Mana Cylix. But I never really liked Mana Cylix enough to put it in a deck. I preferred the version without the cost on the activation but costing instead.