Hello Wazuans,

I need a Paybill Till integrated into my opencart site.
Who has the skills and how much will it cost me?

I can only give you pointers. I am familiar with one method of doing it, perhaps there are others and you will make the appropriate choice after doing research.
There is already a notification system in place. Your paybill is configured on it, and you get a small app which you install on your server. The app (service) is a listener, once someone sends money to your paybill, a transaction is posted to your service. Obviously, some integration is necessary to join the cart side and the payment arriving to complete the transaction -that really shouldn't be too difficult but I will consider it out of scope of my post.

A VPN needs to be setup between the network hosting your server and mpesa's. Also, some sort of license applies I think, since you get the receiving service already made. Give a ring to Safaricom and ask for the Financial Services people, they will furnish all the details.
All the best.