Free with admission to islands of adventure.
If you wish to go to both Islands of adventure and universal studios then you need a ticket that covers both parks.
To expand on Don Johnson's point, as he said its free with park admission to islands of adventure which is from $144 according to universals website ( https://www.universalorlando.com/web/en/us/tickets-packages/park-tickets/index.html). Though I should say when I went prices varied drastically between different sellers and you may find it different cheaper from a reseller.
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