Most IG pools are built with a double lattice of #3 or #4 rebar, and at least 6" of concrete.

As a builder, you can figure local costs for the concrete and forming better than I can. One caution: you'll need to use TRUE 5" slump (or less) concrete, and vibrate it in. If if haven't ever formed long walls before, do NOT try to pour more than 2 -3 ft at a time -- you'll blow out the forms when you do, unless they are super strong. You can do continuous pour around the pool, allowing the concrete to 'soft-set' before you pour and vibrate the next few feet.

But, pouring pools is very old school, except for some very large commercial pools, even though it works OK. Blown in gunite (nozzle mix) or shot-crete (truck mix) has been the standard for 40+ years. However, you'll have to hire a pool contractor or gunite contractor to concrete the pool for you -- the equipment is expensive and not standard in other applications, plus there's a fair bit of skill involved. If you got that route, you can't vibrate. As a result neat, clean and well aligned rebar layout is critical for pool strength; what happens other wise is the mis-aligned rebar mats tend to block some areas behind both mats, and leave voids.

There's also modification of the poured pool, that's been used many times over the years by DIY builders and by inexperienced pool builders: poured bottom with laid block walls. I've seen a number of these pools, and they all worked OK, except for problems above the waterline, where the porous block was subject to freeze damage over the winter. But, if you pour a cantilever deck + bond beam, on top of the block, so the portion of the pool above the water line is concrete rather than block -- you'll avoid that issue.

Finally, don't make the mistake many residential pool builders do. Seasonal expansion and contraction of your deck is primarily horizontal. But, expansion of the pool wall is primarily vertical. This typically results in a continuous, and unrepairable crack under the tile at the water line. The solution is easy: the joint between the deck, and the bond beam must be a full depth expansion joint and NOT a scratched in control joint. Doing it this way, allows the deck to move horizontally, and the wall up and down, without damage.

Good luck!