According to my observations you would need ridiculous resists and armour in order for a full defensive build to even be viable in inferno.
As a full on glass cannon in terms of totally neglecting all resist and go for movement speed and DPS you would still be able to take 2 hits with 28k life and force armour. Also, make up for the lack of defensive stats with defensive spells like my build: http://eu.battle.net/d3/en/calculator/wizard#RcPOQj!dYf!bYZYZa . The rune for acrane orb is deviating depending on the place, like act 3 is more tricky with tap the source but easy peacy with celestial orb. Also sparkflint may be switched for diamond skin when you like to farm to tight spaces like light the signal fires in act 3 which often is ridiculously tight.
So an effiective glass build is less expensive than an effective defensive build, for obvious reasons: You're always looking for more stats in an item like, all res,vit amour and the stuff glass dudes like and more useful stats tends to exponentially increese the cost.
Blizzard have taken measures to fend off extreame offensive as well as defensive builds by introducing enrage timers and increased the chance of reflect dmg affix, like every mob got reflect dmg.
Far far from true, here are my stats wich Ive cleared everything solo infernal with, even Ghom.
17,5k dps (unbuffed)
7500 armor (buffed)
880 Physical resistance (buffed)
700 Resist all (buffed)
-30% reduced damage from melee (together with Blur)
+12000 healing from health Globes
In total Ive spent less than 1,5 million gold on gear. Im using 1 hand wand + Shield. My 1 hand costed me 800k gold, all the rest of my gear was pretty cheap.
I know ppl who are standing no chanse at inferno who are going glass cannon with 40k+ dps and have spent over 10 million on gear, so Id say 100% sure that a Defensive build is both cheaper an dmore effective than an offensive one.
You also wont be able to clear all with an offensive build, vs Ghom and Rakanoth defensive builds are a must.
Also the enrages arent bad at all, I killed Ghom around 5 minute mark, meaning I survived over a minute past his enrage. I also killed Cydaea and Rakanoth well past enrages. They get slightly harder during enrage, but they wont instant kill you like many think. Ghom spawns clouds slightly faster, Cydaea spawns more spiders and Rakanoth seem to move slightly more. Also the enrages from elites are like 10 minutes, Ive only seen elites enrage once ever, and that was a pack of currupted angels in act 4 with ridicilously high hp, and I still ended up killing them.