Gears will be the biggest bang for the buck. You also don't need a tuner, you can just use a speedcal which you can get for 1/4 the price of the tuner but then when you do get the tuner the speedcal becomes obsolete...
Also unless you are DIY on the gear install I'd call around and see what the shops near you want to do them. They SHOULD be $150-$300 at most but a LOT of shops think they are entitled to charge double that or more for no good reason.
2000 Mustang GT Steeda build #48. Bolt ons, suspension, Novi 2000.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.