Hi,
To make a custom communicator, I would recommend Python with hadoop / MongoDB because, they will
1) Provide enough security aspects when it comes to encryption of data.
2) anti-phishing and custom firewalls can be developed to ensure none can hack the messenger
3) Most important aspect is that, this technology will handle numerous amount of data. So we recommend AWS cloud to host the application.
I am however surprised to see the budget because we clearly understand that when it comes to Skype / yahoo messenger type large application development then you should trust a reputed and stable Organization than single freelancers. Because we will start the project from Requirement gathering, planning, System design ( architecture), development, testing with Support and Maintenance program.
Lets discuss in details.
Regards,
Mit-