Paymill payment integration into Wordpress "Pro Sites" plugin

We are looking again for someone to integrate "Paymill" payment into Wordpress WPMUDEV "Pro Sites" plugin. Pro Sites lets you create your own profitable blog or site hosting network, like [login to view URL] or WordPress.com. It offers the users the chance to upgrade their sites and access features like premium themes, plugins, extra storage, domain mapping or removing advertising. Pro Sites works with recurring payments. I'm posting this job again, because the the last developer didn't succeed. Please submit serious proposals and only if you have experience with payment gateways integrations and recurring payments. Pro Sites has already "Stripe" payment integrated which is very similar to Paymill, maybe it will make the development easier, if you could reuse some of the code. Detailed plugin description you will find after searching: wpmudev pro sites or under [login to view URL] There is also a Paymill plugin for Woocommerce, it's of course not compatible with Pro Sites but maybe you could use Paymill library files from there. As a final product I expect you deliver me Pro Sites plugin with integrated Paymill payment. The integration shouldn't break any feature of the plugin. It should work like already integrated there "Stripe" payment but with Paymill gateway. Could you please give me your cost estimation. Let me know if you have any questions or need more details.