Single-threshold shower pans are used for alcove showers (showers enclosed by walls on three sides) and double-threshold shower pans used for corner showers (showers enclosed by at least two pieces of perpendicular or angled doors or inserts).
Shower pans generally run around $300. They are generally more expensive than tile flooring.
Costs vary greatly by region (and even by zip code). To get free estimates from local contractors, please indicate yours.