Reroll costs can be absolutely savage. I've just burned over 10 million credits and 100 machine god's spark trying to tidy up the affixes on a weapon to make it usable. I've been playing for a while so I managed to afford it (though I don't have much left) but certainly for newer players this would be way too much.
It would certainly help if we had some idea of what affixes could actually be rolled and maybe a percentage chance. I've lost count of the amount of materials I have wasted on fruitless rerolls.