**A prebooked GoOpti shared shuttle is the first option I’d try** for balancing speed and cost. It offers direct transfers from both Portorož and Piran to Ljubljana Airport, including collection from your accommodation. The route pages advertise fares **from €14**, but that is a starting price, not a quote for your Sunday. [Portorož transfers](https://www.goopti.com/en/transfers/slovenia-portoroz/slovenia-ljubljana-ljubljana-airport-lju), [Piran transfers](https://www.goopti.com/en/transfers/slovenia-piran-main-bus-station/slovenia-ljubljana-ljubljana-airport-lju).

When searching:

- Select **Ljubljana Airport (LJU)** as the destination.
- Set your required **arrival time**, ideally around **9:30am** to leave some margin before your 10am deadline.
- Choose a shared transfer and allow an earlier pickup if that reduces the fare. GoOpti says advance booking and flexibility generally give better prices. [Booking page](https://www.goopti.com/en/transfers).

The budget alternative is a **regular bus to Ljubljana, followed by an airport bus or shuttle**. However, I haven’t verified a Sunday connection that gets you there before 10am, so I wouldn’t rely on it without checking both legs for your exact date. If the direct shuttle is expensive, another practical option is to travel to Ljubljana on Saturday evening and stay overnight. [Coastal bus information](https://www.portoroz.si/en/general-information/getting-here/by-bus/).

**Which year is your Sunday, 12 March?** That’s needed to check the correct timetable and availability; current fares and schedules may not apply to your trip.