price comes down to brand, quality not so much. If you're dead set against a sub then the best bass you can get from a door speaker would be 6x9's with a dedicated amp for the two of them, however those won't fit in your rear doors and custom work will be required. So it comes down to what you want out of your speakers, if you want booming bass, use your sub and deal with it....if you don't care so much then just get a set of speakers that fit, amp them and tune it to your liking and be set that way. You will not find a speaker that's less than 7in diameter that'll be a replacement for a dedicated subwoofer system.