Why does a good recording cost more to make than a bad one? and why do I pay the same price whether it's good or bad?
Your not paying for the audio quality, you're paying for the intellectual property of the artist, that's determined by what the market will bear for that particular artist at the time.
In a typical session, you need to mic instruments. You can easily spend many hours, even days on just a snare drum, (if you were really a perfectionist type) adjusting tuning, changing drum heads, changing snappies ( the wire thing on the bottom of the snare), muffling heads, trying different mics, different mic postions, different room placements, and room treatments, around the drum kit, just trying to get different sounds.
If you are paying session musicians to stand around while all this is going on, this adds to the cost as well.
This is "engineering" in studio lingo. At typical studio fees, a scenario like this could run thousands, upon thousands of dollars. And we're just talking about a snare drum. In pop recordings, one snare drum sound will not always work really well on every song, and then the process begins again.
That's just one instrument of many that need to be engineered to make a typical pop recording. Doing multiple takes, and compiling takes to make composite tracks (where a performer records many different takes of the same part, then you edit between the different takes and make a composite track that are segments of the various takes strung together to make an ultimate "take". This can take many, many hours.
Then you come to mixing. You might have engineered every individual sound to be really clean, full, dynamic, and clear, but that doesn't mean it'll blend well in the context of the song. You might need to pull bandwith out ( take out bottom end, pull out some mid-range, de-emphasize the treble) or post process (add compression, reverb etc..) in order to make the instrument blend well overall. Mixing often times is full of compromises, and you can't always have your cake and eat it too. Often times, something has got to give, in order to best serve the overall mix. This is part of the mixing process.
Mixing one song can take a few hours, up to many days, depending on the complexity of the music, number of parts, and just what end result you are trying to achieve. Often times, there is one "type" of mix done, then a different one of the same song is started from scratch, with all the faders and knobs, set to zero. Sometimes people do multiple mixes (5 or 6). Sometimes they send the session tapes out to have a big name producer or engineer do the final mix, before it gets sent off to mastering.
Then there is mastering. A lot of time can be spent there, tweeking and so forth.
Those are the main ways recording sessions go. Time is money, no matter how you slice it. And it's easy to wrack up a huge bill.
I don't understand why a good recording wouldn't also sound good on crappy playback equipment...and stellar on good equipment.
Because the playback equipment is crap. Distortion. Good equipment won't make a crappy recording sound good. You'll just hear the crappiness clearer.

A good recording on crappy equipment, will sound a heck of lot better than a crappy recording on the same crappy equipment.
IMHO redbook can sound damn good, but typically doesn't. enough said.
Yup. It can sound really damn good. Amen, brother!

Cheers