Convert single tenant web app into multi-tenant SaaS enviroment

have a standalone,traditional web based app written in php that uses mysql database. My client would like this app converted into a SaaS application as cheaply as possible,using one of the three methods below. Need estimated cost for each of the following methods to see which is cheapest to have implemented for my client. Please see the following three options listed below. Im looking to implement just one of these methods, but would like estimates on all 3 so can discuss with my client : Option 1 – Single database, single code-base Use a single database and store all client data in a single database. You will have to add a field like “clientid” in all your tables and modify all your SQL queries to select the correct “clientid”. If you already have a single tenant app, then heavy modification is required in the code. Option 2 – Multiple database, single code-base Create a separate database for every client. No modification is required to your existing single-tenant codebase. You will only have to modify the configuration file to select a database depending on the client. Option 3 – Multiple database, multiple code-base Create a separate database & duplicate the complete code for every client. No modification required at all. ------ on another note, if there are any other cost effective methods to achieve this same function , please suggest along with price estimate.