It is hard to give a definite answer to this question for several reasons. First, what is PHP web development? It is a complex process that involves multiple specialists and the use of advanced technological tools. The number of specialists and the kind of tools depend on the project’s scope, which in turn depends on the objectives.
Thus, upgrading an application with a new feature may be considered a short-term project (1-2 months) requiring one or two PHP web developers. Whether you hire a freelancer or contract a PHP development company, you may pay from $6,000—$15,000 to $10,000—$25,000. If you hire a PHP development company in the USA, you’re likely to pay more than with a specialist from an offshore country.
A legacy software upgrade or building a product from scratch may take 6 months to over a year. In this case, expect to pay $50,000—$140,000 or more. Remember that these are ballpark figures representing average values across industries and locations. Contact your vendor with a detailed task description to get a precise estimate.