: If you have holes in it, it is probably an enameled steel tub, rather than cst iron. A good cast iron tub costs about $250; ( a steel tub like you have is about $110); an excellent alternative to the cast iron is one called Americast; has all the quality features of cast iron without the weight..price is similar.
By far the larger expense in this job is the labor in getting it done. Get some references in your local area; expect to pay $500 to $1500 for install. Depends on the wall material, etc.