The problem is that Universal tickets are priced dynamically, meaning that depending on what day you're going the prices could well be different to the day before or the day after. Now the following prices are taken from the Universal app, but I have a feeling these would also be the gate prices as well - there doesn't seem to be a discount for buying online, it's just a way of guaranteeing you have your tickets bought in advance so you don't need to queue up.
A 5 park visit ticket (where all visits have to be used within 8 days of your first park visit) for all three parks, plus with the ability to visit more than one park per day, would set you back $516 (£415ish) if you wanted it to start today, $464 (£375ish) if you wanted it to start on the 25th April, $502 (£405ish) for 25th July etc. Lowest price I found was $420 (£340ish) for a ticket starting on 9th September (highest is $564 over the Christmas period).
If you only want to do one park per day (e.g. no hopping and so can't use the Hogwarts Express), then that tends to bring the price down by about $70 (£55ish) in total.
