Customization work of already existing Real Estate Portal based on CodeIgniter Framework

We already purchased an open code script based on CodeIgniter Framework and there's an API documentation available. We are looking for PHP/MySQL developers who are able to customize a real estate portal for us. We would like to buy following real estate script: [login to view URL] It is open code and allows developers to work on the site. Here's an overview: [login to view URL] Here's the demo that you could check how the software looks: [login to view URL] The first step to program would be following: Here's an example for a customization work: There should be an alert sent out to registered members of the portal who tick some regions in their admin for which they would like to receive an E-Mail alert once a new apartment for rent/buy is being posted. If clients save an alert subscription (they can also save a subscription but they can also activate alert subscription or deactivate alert subscription), it should cost a subscription price which can be defined in our admin. It should be possible to define in admin the different costs for subscription, define for how many days a subscription is valid with its costs, also define weekly or monthly (monthly means not always 30 or 31 days, it would mean e.g. if someone subscribes on 17th Feb 2015, it will expire on 16th March 2015, even it's only 27 days). As monthly subscription should be cheaper than weekly subscription, it should be possible to define in admin different costs for every subscription that user would have the choice between various subscriptions (e.g. user could choice whether he would like to subscribe e.g. for 1 week e.g. for USD 5.00 or if he would like to subscribe for e.g. 1 month for e.g. USD 15.00). Summary of what needs to be done: 1. Create a new paid services template for alerts with following settings: - period (days, weeks, months) - cost So it can be used to to create several packages with different price and period - paid subscriptions. 2. In user interface you will add a section with a list of saved searches with following options: - Subscribe. After clicking this button, if user has no paid services, he/she will be redirected to the page with available paid services. - The user purchases it and choose optionally whether it is recurring payment or not - Unsubscribe option. After clicking this button, user will see unsubscribe immediately or unsubscribe by the end of a period. - If subscription period ends, the software will check whether user chosen recurring payment or not. If yes and user has enough money on the account, the software will automatically take credits from the account, after what user gets e-mail alert. If user didn't choose recurring payment or lack of money, subscription will be removed. - User will get alerts on each new listing published under his/her saved search. We have a lot more programing stuff to do for this portal, this was just an example of the first step we would like to have programmed but we don't want to publish here what else needs to be done, can you please let us know how much this described programming work would cost (we pay in 3 milestones, 1st milestone we pay after you have created the template in user interface where user can subscribe for alerts and redeem credits, 2nd milestone is that admin can amend all subscriptions of users in admin panel, 3rd milestone is we pay the final amount after successful testing. Important is that everything should already work perfectly when you give it to us to test. Thanks