You can purchase the combined ticket and unlimited express pass. It is WAY cheaper doing it this way.
https://tickets.universalorlando.com/Ticket-Store/PurchaseTickets.aspx?VIP
It would be $354.99 if you buy the buy 2 get 1 free ticket plus express. That gives you 3 days of express. It says valid any three days from March 29 - April 11.
It is pretty simple to figure out on the website. I'm not sure why there is such confusion here. Just click on the ticket you want and then a calendar will come up where you click on the first day you are going to use the tickets and it will highlight three days and give you the price.
Then you add it to your cart. At the end it will come up with price included taxes which is $378.07
If you do it separately, it would cost $389 + tax for just the express passes and then over $200 for the ticket.