I was wondering, if I get the Extra effect enchanting perk, and enchant my weapon with say.. absorb health and absorb stamina.. will it have twice the charge cost compared to if I only had absorb health? Already tried searching on google, but couldn't really find an answer to it... not on any wiki either.

Pretty sure it only factors the first enchantment. A good way to test this would to be putting two enchantments on a weapon, one in Destruction (like Fire Damage) and the other in Alteration (Paralysis) and equip a full set of Fortify Destruction enchantments. See if the weapon loses its charge. Then switch to an Alteration reduction set and do the same.