Don't hold me to the exact dollar amount, but I will be close, as we have done both of these options...
If you want to do a taxi on your own, it is $35 each way from a Disney resort to the drop off spot at Universal. That is for up to 7 people, flat fee. You don't need an advance reservation, just go to the cab stand at your Disney hotel and they'll have a cab for you in a minute.
If you want to do the Mears shuttle, it is $8/pp each way. You can book that through your Disney hotel concierge.
Be advised it takes MUCH longer to do the shuttle, as they will stop at multiple hotels. About 25 minutes via taxi, as much as an hour with the shuttle.