On Steam the DLC only costs $5 each as opposed to $10 when it was brand new, I thought it would be the same on consoles. If it's still $10 on the 360/PS3 I'd contact Bethesda directly (I don't think any Bethesda employees actually frequent this particular forum), because it's odd that the DLC would be half price on the PC now, but still the original price on other platforms.
If all else fails, you can probably get the Game of the Year Edition for $20 at this point, which is cheaper than buying all DLC half priced anyway.