Plant Extension Cost

I was recently quoted a price of $5900 to run a plant extension to our new house.  The total linear feet of line was around 649 ft.  However, less than 2 months ago, the estimate came in at $2616 for 500 some-odd ft.  Can someone in a management or supervisor role tell me how the price more than doubled in less than a month?  I was also told that Xfinity would split the cost with me (the customer).  In my opinion, this is a ridiculous amount to have to pay up front.  Management PLEASE HELP ME SOLVE THIS.