Controversial opinion incoming: Forget the rears completely. It's a waste. Spend that money on better front speakers, sub or a DSP.
I am complete non-believer in rear speakers, even more-so after my recent upgrade. OEMs install rears simply to fill the cabin with volume without taking up cargo space with a sub. If you want quality sound and have a limited budget, just buy nicer front speakers instead of rears and add a real subwoofer. If you were going to buy 2 $125 pairs, drop the rears and spend $250 on a nicer front. If you were going to buy 2 $250 pairs, buy a single pair for $500. You'll hit start to hit diminishing returns once you get beyond $400-700 per pair, IMO, but up to that point you generally get a LOT better sound as you increase your budget per pair.
Last year I completely redid my system. At 32, this was the first system I'd ever really spent money on, despite being an audio fanatic through my 20s. I shopped speakers and found nothing better than the Morel Virtus Components. Huge detail in the tweeter and smooth mids. Those speakers are simply incredible. I don't think Focal had an equal offering until their $800-1000 pairs (The Morel's were $450). It's a mental shift now listening to music. You can hear the nuances of snares, toms and cymbals soooo much better. The amps and distorion chosen for guitars or the resonance in an acoustic is unreal. There's a wealth of detail and richness you just can't hear with your average $100-200 speaker. Listening to old Metallica was like hearing it for the first time again. That snare in the Black album is a cannon and prior to having these speakers I never knew it. Voices are so rich and full. Everything from Jewel to old school thrash metal to electronic is so much better. Pink Floyd, my god. Nothing beats a drive home after a long day like good music on a good system.
I also added a DSP amp (Audiocontrol D-4.800), but the real upgrade difference was alllllll in those front speakers.
Do yourself a favor a spring for the fronts. No matter what you do to a system, you can't improve anything more quickly than upgrading the front speakers to something a tier above typical "Best Buy" speakers.
That post got away from me. Sorry for the wall of text. I'm passionate about audio, it seems, haha.