Why was Christ's sacrifice such a big cost? Many hymns refer to the immense cost that Jesus paid on the cross. In one sense this is consistent with evangelical theology in that Jesus was taking the sins of the world upon himself.

But some songs use phrases like "You gave up everything for me", or "So infinite the cost". What can that mean? Presumably it must be either the Incarnation or, more likely, his sacrifice on the Cross, right? But, well, Jesus rose from the dead 3 days later, and ascended back into heaven 40 days after that, going back to the Father. 

It always seems to me that Jesus, the Word, the Second Person of the Trinity, had spent a long time in heaven even after Earth was created before his first coming (at least four thousand years and possibly millions); he's spent at least two thousand years between his first and second comings; and will have eternity with the redeemed praising him after the second coming. So why is spending 3 days (or rather 1-and-a-half days) separated from the Father, or even 33 years on earth, such a big sacrifice in the grand scheme of things? Even more so given "a thousand years are like one day to the Lord".

I'm most interested in answers compatible with a (British) evangelical position, but up for helpful answers from anyone :)
I think Philippians chapter 2 shares some good light on this:

5 ...Christ Jesus,

6 Who, existing in the form of God, did not consider being equal with God a treasure to be grasped,

7 But emptied Himself, taking the form of a slave, becoming in the likeness of men;

8 And being found in fashion as a man, He humbled Himself, becoming obedient even unto death, and that the death of a cross.

To go from Creator to creature, that's a big cost. But He not only became a creature, but He became like a slave among men. Even if He were to come down and be a king, that's still a big cost, but He was mistreated, hated, and abused by the very people He was doing so much to save. That's quite a cost. After all His living and work on the earth, His closest disciple, Peter, swore and cursed, saying he never even knew Jesus, right as Jesus was being tortured, and about to be crucified. That's quite a cost.

There's the physical pain, too. I've heard that when they whipped people, as they did Jesus, they had to count out the whippings to make sure the people didn't die. They also had a doctor stand by to make sure they can survive to continue in the whippings. He didn't drink for about 24 hours I think in that last day, and He lost a lot of water when He was bleeding out. His hands and feet were nailed with big, rough (not factory made) nails into a cross and He was hung from these wounds. The way they put people on the cross means you can't breathe properly, so you have to pull on your hands to lift up your torso for every breath.

But in all these things He never cried out. He only cried out in the last moment, to say "My God, why have You forsaken Me?". This indicates that with all the sin laid up on Him, God the Father turned away from His Son, and that was worse to Jesus than any of the humiliation, rejection, betrayal, physical and emotional pain that He suffered up to that moment.

I used to think that it wasn't a big deal, if Christ could just resurrect again, it doesn't matter if He dies; but I think it's much bigger a deal than I'll ever know ;)