Kits are going to be more expensive....you are paying for the cutting done by someone else. A basic kit with yardages of fabric will be less expensive than a kit that has smaller pieces of fabric...less cutting.
But, if you do not have fabrics in your stash, and need to shop and buy fabric, sometimes, kits can be the "better deal." You can get just the bits of fabrics you need in the kit.
I have always not been a kit person...I like my quilts to be unique...not the same colors as anyone else...maybe similar...I do have a large stash, and prefer to work from it...but may buy some of the fabrics that I see in a quilt that I love.