I too would caution against being sucked into the so-called "arms race", where you feel you must splurge on expensive rares to round out your deck and make it more effective. While I was still playing years ago, I was able to make decent decks entirely out of commons/uncommons for under $10 each. I wouldn't say they were the best, but fairly good for the money spent, and still able to win a fair amount of the time.
I did want to mention that, after playing in the prerelease this morning at midnight, I think Eldrazi would be an absolutely great set to bring a new player in on. The slower pace and bigger spells and creatures are probably good for keeping the interest of new players, and there aren't really many mechanics which seem very complicated.
Honestly, the introduction of all these huge creatures that pretty much signal the end of the game when they appear worry me, since I don't like the idea of gameplay being dictated by whoever plays the largest creature first. I personally prefer a faster paced, attrition-based game where smaller weenies trade blows with fast burn and cheap counterspells.
I have been out of touch with Magic for quite a while now, but how prevalent are abilities which let you directly put creatures into play without paying its casting cost? Back then, we had call of the wild, show and tell and reanimator decks which can easily sneak such beasties into play by 2-3rd round.
It seems to me that all these exorbitant casting costs will simply encourage players to find ways and means to get around actually casting them the old fashioned way. Maybe I am just outdated, but in my time, a game's outcome was more or less dictated by the 6th round.