There are a few ways to demo a pool. I build new pools and many times when a client wants to reconfigure a pool (make a curved pool into a square one), it's easier to rip one out. A full tear out runs $10-20K. It really depends on access, how much is being removed. I had one pool where they shell of the pool was 18-24" thick (instead of the standard 6"). We suspect the builder dug the hole too big and just used shotcrete to 'fill' it in. Our demo guy worked for free on that job.
There is the full removal and proper compacted backfill to make it all go away. This is the most expensive. This is needed if you are building a new pool in the area or a structure over it (like an R/V garage). On a big pool with bad access, you are getting closer to $20K. But typically you are in the $15K range. On really bad access (like through a home with zero lot lines on a lake), you can get really high.
The second way is to punch some holes in the floor of the pool and tear it down to about 18-24" below grade. With good access, you're below or at $10K.
The last way is to punch some holes in the shell, back fill it, and build over it (like a deck or something). I've done a few jobs like this. Instead of spending the money on demo, you get some landscaping. You do have to be creative and the pool needs to be in a decent location. I've used old pools to act like a retaining wall and built a recessed deck area. I've also built pools right next to an existing back filled pool.
On the prices, I rounding up a bit as I am only aware of the wholesale pricing. These are demo guys that we send $250K worth of business a year, so we get a different pricing structure than a one and done deal. They don't deal with retail clients for the most part as there are days and days worth of questions vs. a job order. These prices are about what we charge retail with building a new pool. Cost is dependent on the scope of work we are doing. For example, if I'm building a complete backyard, there is a slight discount to demo the pool.
One guy that I have dealt with that will deal direct is Drew Zanga with Heatwave GC Inc. (602)-531-0300. It's been a few years since I've dealt with him, but he did good work and kept to his bid even when the job got tough. He definitely liked to talk. I like to talk and that dude blew me out of the water. But he did good work.
As for remodeling a pool. You don't save much money over building a new one. You still need to do much of the work and typically add something to it while you are redoing the pool. A simple chip out and new interior is $10K. But a full remodel (new equipment, adding a water feature, adding a baja shelf, or converting a diving into a play pool, etc.) can easily get to $50K-$75K.