Check your wiring diagram and the old speakers--were these 8-ohm speakers running parallel with 8-ohm rear door speakers, or were they 4-ohm?
You may need to rewire, add channels with additional amp, or do some fancy crossover work if you are replacing an 8-ohm pair with 4-ohm. If your sound is fairly good without them, you may want to look at replacing them with a mid-bass you can adjust separately with a fader.
Quality/price? For what the dealer wants for a pair, you can add an amp and replace half your speakers with MB Quart component sets. However, for all around use, unless you are really picky and have the perfect ears to match, you can do very well with Polk, Infinity Reference, and any of half a dozen other good brands. I suggest you check Crutchfields for prices and specs(watch their "this fits your car" tho. Do your own measurement!) and then take a look on ebay.
I picked up a new set of 8" Polk mid-bass speakers for about $80 for the rear deck of my '99 S70, and they really add a bottom to the music without needing to be "punched up" or boosted.
Also run a search on this site under speakers, or stereo, or radio--lots of good info already available.