I think it's 25 spirits for earths and 50 for bloods? Most servers bloods go for 200G+ easily so it's more efficient to change them.
If you want to farm primal spirits just for crafting you'd still be better off getting gold and using the AH if you have an active and liquid market for it, but like dellza said just get any of the primal spirit profiles on the forums, there's tonnes out there.