I have previously had the Amazon Prime free 30-day trial twice. Since then, whenever I've clicked through on the 'Try 30-day FREE trial' I'm only given the option to pay £79
This morning I was about to purchase a last-minute xmas gift I need for tomorrow and so I selected Next Day delivery - I continued to review my order before placing and I was given the option of a 30-day FREE Amazon Prime trial :)
I didn't place my order in the end but I did sign up to the free trial!
This may help others - just try and order something that is Prime eligable - I was going to order the Glenmorgangie Whisky (it's their deal of the day currently).
If it doesn't work for others then obviously vote it down to stop others wasting their time ;)