I would second Mega for the battery source.
If you are diving with an operator, they may get a discount at Pro-dive, or another shop. When I lost my mask....yes, I was THAT guy.....I got a discount on an aqua lung mask at Pro-dive because I was diving with Blue Magic. that made it just a few dollars higher than leisure pro prices. (Only mask that fit) A computer battery won't make that much difference, but on a $100 mask, 10 bucks made a ouch difference to cover a burrito at Burritos Gorditos and a Bohemia Obscura.
wish I was tHere....woke up to an inch of ice, sliding cars, frozen cattle troughs, and....work. Have fun!!
Jay