I would like to know what would be the price for a washer machine box installation.

If you specify what this all will entail in your specific case, it will be possible to provide an example price. Without that you ask for some kind of magician to prophesize...

What type/brand of washer?
Install in what?
What access is available?
Are electricity , water, and sewerage pipes already available there?
Etc.

;)

That would depend on a number of factors:

New installation?

Upgrading existing installation?

If upgrading an existing installation, is it plastic or steel drainage piping?

If upgrading an existing installation, is the existing trap and trap arm sized correctly?

Does your local authority require shock arrestors?

Is the existing water supply copper, plastic or steel?

If it's a new installation, how far away are the existing drainage, vent and water pipes from the desired location?

Growler's bang on! There are many factors involved in giving a estimate. The biggest is that you have to be on site to see for yourself what material it's going to take. Then there's labor. Union or non-union? Different areas have different labor rates. In short, it's impossible to estimate a job setting in front of your computer. I would call around and get three estimates. Good luck, Tom.