For the little bit of seed you need for your yard, online is your best bet. You don't want the builder's mix, that's probably the lowest grade seed there is.
The best process to seed for you (without me seeing the yard) is to aerate and then rake with a steel rake. No slice-seeder, bermuda seed is tiny, it need's to be on top of the ground. A slice seeder would plant it too deep and it wouldn't grow. No straw either. It's much more important that you keep that seed wet, don't let those seedling's dry out, they will die, fast.