Cost is searched in two forms. What it costs to build and what it costs to run are different questions from the same person, and a company answering both is present at the beginning and at the decision.
Permission questions arrive early. Whether consent is needed, what the boundaries and depths imply and where a pool cannot go is read months before anybody requests a quote, which makes it the cheapest way onto a shortlist.
Comparisons decide the specification. Concrete against liner, indoor against outdoor, heated against unheated: each of those comparisons belongs to somebody who has already decided to build and is now deciding how.
Renovating an existing pool is barely served. Retiling, a new liner, a modern plant room or a heat pump conversion belongs to an owner staring at a pool nobody has swum in for three summers, and almost nobody writes for them.