I'm reading the premium has 4ohm tweeters, &
(just to make sure does it have?) 4 mids, 2 in the front 2 in the back.
If so,
all four mids are 2 ohm getting about 20w RMS each. (that's nothing).
That amp (like most factory amps), puts out as much power as the cheapest aftermarket head units do. It's doing next to nothing.
If you want the absolute cheapest set of speakers you can find, don't need em to get loud, (as in you only listen to it with an inside voice volume), then you need some 2 ohm 6.5 mids that are 20w (or as close to that as you can find. For the rears you might have/want two-ways instead. I wouldn't be surprised if you can only find 30w, or a hair more.
If your head unit doesn't have GPS, I would guess you would be better off buying a new head unit. Hopefully you want an amp, with new speakers that are either rated at the amp or at the head unit, and running new wire either way. You will get more volume out of this with a head unit that does at least 50w x 4 RMS. You could still use those tweeters if you were dead set on it. Although you would want a crossover, and a better option would be a set of components and replace the tweeters.
The cheapest option, 2 ohm 6.5s as low wattage as you can find probably about $100 for two sets.
The next best budget option is a new head unit (if you don't have GPS) with new speakers, probably closer to $300, and with an amp you will get a lot more volume, (you are maybe getting half now what you would with just a small 100w x 2 or 4 amp), and that's about $400 or a little more (payin retail).