If you are gonna replace them then you need something to push them bc the factory speakers are bose and have a built in amplifier. You can either get a CD/reciever head in unit that will power it or get a seperate amplifier for them.
Anyways, I replaced my 6x9's with Pioneer 3-way speakers that cost me about $70. They have a good amount of base and great highs and mids. I actually got them at Walmart. After listening to many 6x9's I thought they had the best bang for the buck. But, I actually almost got some Jenson 3-way speakers. They were like $50 and sounded very similar to the Pioneer's. If you want something better than these then I would go to some place like HIFI buys and have them show you them-listen to them- find the ones you want- then shop around for prices.