How much does underlay cost?

Floor underlayment is most commonly 3/4 inch plywood, often with lapped or grooved edges. This material is about $25 to 30 for 4 ft x 8 ft sheets at large home centers.

Underlayment used to level an existing floor is usually a better grade of 5mm or 1/4 inch plywood. This costs about $10 to 15 per sheet.

Installation of the material costs quite a lot more than the material itself. It is a fairly easy project that most experienced household handymen can do themselves, though a helper is sometimes needed with the heavy 3/4 sheets.

You will also need a floor glue, construction screws, and most often a nail gun. Shims are helpful unless the existing framework or floor is perfectly level (it never is). Many less-than-perfect contractors save a little money by skipping the glue and screws, but the homeowner will suffer the squeaky consequences of that cheapness.

Do it yourself cost for 1000 square feet: About $1,200. Maybe $700 for 1/4 inch over existing flooring.