Dont you want to run big wheels? I would get the wheels under the car before deciding on amount of drop. Then you know how far you can go and wont limit your wheel/tire combo based on where the car is after being lowered.
But you have a bunch of options. Bags, cut your stock springs, buy lowering springs (eibach, hotchkis,etc), yank some b-body spindles from the yard and buy some moog springs and then cut those, etc. Your approach would dicate the cost...so how tricky you wanna get?
But if you dont have your wheels yet I would get those first and then lower depending on how much room you have with the wheels that you want to run.