Yes, as Bunzy said, most of the cores are more expensive than the actual crystals.
Core morphers in the AH go from 50,000-1,000,000 gold.
(Psi went for 981k before the crystal reset.)
So the AH bidding prices can range from (if the shard ratio is still 43:1 selling) 1163 crystals to 23256 crystals.
However, again as Bunzy said, they are typically around 250,000 for the more sought after classes.
So this means your entire class change will cost somewhere around 5814 (AH bid) + 2800 crystals (CS item) = 8614 total crystals.
Also, keep in mind, that to actually USE the item to change classes, you are required to either USE all your upgraders in your bank or discard them. That means, if you have a lot of gear in the bank that you are meaning to upgrade, you're either going to have to go on an amalgam farming or purchasing binge. On top of that, gear upgrades are stupidly expensive. 500~715g/ea upgrade. Therefore, you have to factor that in. Oh also, if you need to uncurse anything, you'll have to factor that in too, or just discard them.
Good luck.