The stock dash speakers are like 3.2 Ohm. So 4 ohm replacements should be fine on the factory amp. Would be a little lower volume, probably wouldn't make much difference. But yeah, I probably wouldn't drop a lot of cash on any speakers unless you were considering adding a Amp later. I would bet almost anything will sound better then the stock speakers. With the stock amp I don't know if you would notice a ton of difference between 60 dollar speakers and 300 dollar ones.
Btw FWIW, when I traded my 22 in on my 24. I drove 8 hours there and 8 hours back. I removed everything from my 22 except the tweeters I added to the A pillars. Just those make a big difference. Stereo sounded way better on the drive up then the drive back home without them.