Hi Michael,
At the outset to merge you application with the CakePHP we should know the functionality of both the applications to check whether they both can syncs together or not, When it come to conversion part the code you have it might helps up to some extent in rewrite/re-code, developing in CakePHP framework and understand the functionality so unless until if we don't have proper information about the above elements we cannot determine the ($$) price and efforts required in performing you task, We hope our message make some sense we will be glad to resolve and help if you come up with questions and project details.
Thanks
Ben
Project manage