Can't go wrong with soundqubed if your on a tight budget, a few hundred dollars could have you a sub stage, and if you like the factory radio you could get a line output converter and just use the stock mids, and add a sub stage, as it will be the most noticible change. Then later you could always upgrade a piece at a time. Second thing I would do is change your factory speakers, then after that you could get a amp for your mids, highs.