Bulk SMS - Cheapest Price possible. Over 500k

hi, I have over 500,000 UK Mobile numbers who I need to SMS in one hit. I willbe asking the receiver some questions and if they need to answer yes, they can reply to the message and the reply needs to come to my email. I need the absolute lowest price to send the SmS as I will be looking to do approx 100,000 every week. want to start soon. so come back to me ASAP