Calculator, Pencil, Paper
Batman and Catwoman would be good costumes for a husband and wife.
At your home make costumes that you like from tv or books if you don't know how find someone that is really good at making the costumes. Good ideas for costumes are naruto character costumes or any other costume you like.
You can find hundreds of good quality costumes at: "http://www.mrcostumes.com/". Make your child happy with the variety of costumes this website has to offer.
Some good ideas for costumes for couples include Marge and Homer Simpson and Lucy and Ricky. They make for great costumes!
He is good at math
"Value Village" is a good shop with cheap,and stylish costumes. Although the most of the costumes are second hand, all of them are in good condition and set at a cheap price.
You can find the costumes at wholesale prices, used one also at wholesale Halloween costumes shop.
Elvis is a good costume
There are many good ideas for costumes depending on the likes of the individual. Costume ideas include, dragons, witches, and princesses.
Costume Castle
Wicked
Try partycity.com.They have a bunch of costumes there, but maybe not the one you want.