When shopping the Swap Meet, check all the prices before you buy. You can find one place that has great prices, but go a bit further down, find the same thing for less. Just a word of advice.
As to fabric buying in shops....
Fabric Mart in Pearl City, right behind/beside Cutter Ford. I loved that place...their cuts are great.
Walmart is good, but I liked the Pearl City store best. Been a few years since I shopped there, but I'm sure since Oahu isn't that big, you can hit all the Walmarts and check.
Kaimuki Drys Goods....OMG! LOVE THAT PLACE!! I would tell the women there that they were evil because I always bought more than I had expected to buy. lol
Kuni Island Fabrics on King Street, not far from downtown is a nice little store. If you go too fast, you'll sail right by it. It's right next to a flower shop and I think you have to turn right onto University (if headed Diamondhead bound) and then quickly turn right into the parking lot.
The Calico Cat is a great little shop too. It's on Koko Head .. (808) 732-3998 Give them a call and they'll give you purrfect directions to get to them.
These were my favorite places I would go to when I lived there and then would go back to when I went to visit.