PHP and wordpress Developer

Hello I need a PHP developer who can work with us full time for a couple of months. We want to integrate multiple PHP applications. We will use wordpress to sell the packages and to allow users to access the applications from here. Any other suggestions are also welcome. All the applications have their own login but once users sign in to our wordpress website (or we can create something in php) we want them to be able to login to these other applications directly. Please contact ONLY if you have experience with such single sign on or have worked on any portal where you provided such integration but without breaking the core files (I would like to be able to update the applications with minimal custom changes needed at every upgrade). Budget per month is 600 USD. If you can complete it in a month then we will pay bonus of 100 USD. The budget is not negotiable so please don't bid if you find this low because this is the most we can afford right now. This is no disrespect to those who charge more. You are obviously worth it but we have budget constraints to work with. If we get a good experience, you can expect to continue work with us on at least part time basis for a couple of months with a good chance of ongoing full time employment. Thank you for taking the time to read this. When you apply please give us information about any other similar integration project that you have worked on. As mentioned previously, we really want to work with someone who has the experience and not someone who will learn on the job.