Fencing needs to meet certain building codes and ordinances when a pool is being surrounded. Wrought iron would be prohibitively expensive when made to meet these codes.

Wrought iron doesn't flex to meet the ground's undulations and that would leave gaps at the bottom and the tops might not align nicely. It is not as maintenance free as the others as it will rust, especially near the bottom. Painting will be needed periodically. Replacement sections are very expensive.

Pressure treated wood and aluminum have some of the same issues as wrought iron but the material costs, replacement costs, and installation costs are substantially less.

Aluminum doesn't rust either. Typically, it's a painted surface, usually black, so it looks like a wrought iron.

Vinyl fencing is also lower in the costs than iron is. It comes in both different colors and patterns.

Chain link and vinyl coated chain link's opening must also use a pretty tight mesh. This keeps little hands from becoming trapped. You can see through it, unlike wood or vinyl.

In general, the verticals and horizontals of any fence must be tightly spaced to prevent a little one's hands, arms, or head from becoming entrapped. It must be non-climbable and most places require a self closing gate gate with a latch that children cannot reach.

In general, a fencing contractor is going to be less expensive than a pool builder. One price does not fit all available options. The price for materials and installation is going to vary. Home Depot and Lowes materials tend to not have the same quality and a fencing contractor. There is a substantial delta in the construction of the materials used and installers used.

Scott

A good rule of thumb for a compliant pool barrier is 48" tall minimum, gates must swing out and both self close and self latch. Note, some cities vary on what they consider compliant and may request 60" tall with a thumb latch at 54". We deal with both in our area depending on where the pool is being constructed. On an iron or aluminum fence the pickets must be 4" on centers, this leaves 3 1/2" of air in between the pickets.
I suggest aluminum over wrought iron but if you like wrought iron, purchase powder coated galvanized iron. It does much better in wet climates than standard wrought iron for longevity.
Your price on aluminum is in the hunt but cedar should be about 20 to 25 per foot if your have 100'+-
If you have 50' or less the price per foot will go up, gates should be 150 wood and 300 iron.

See ya,
Kelly

Wrought iron is by far the most aesthetically pleasing, highest maintainence and most expensive choice. If you don't mind the patina from age it will last a hundred years with some effort. It can always be wire brushed and painted. If you can't handle a scratch on your car it probably isn't your best choice.