Gorontalo is served by Garuda Indonesia, Lionair and Sriwijawa. Gorontalo airport is a good hour-long drive from the main town. Kijangs run on a share basis into town, costing 70,000 rupiah per seat.
There is one bus a day that runs from Gorontalo to Manado, leaving at 05:30 and costing around 100,000 rupiah. The trip takes 11-12 hours.
By Kijang, seats go for 200,000 rupiah (front seat), 175,000 (first row) and 150,000 (second row). Scheduled Kijangs leave at 08:00, 10:00 and 14:00, though you can charter your own at any time of the day should you wish. A charter to Manado should cost around 1,200,000 rupiah, though will cost more on public holidays.
The trip takes eight to nine hours depending on traffic and how wild your driver is. Whether you just have a seat or charter the entire vehicle, they'll pick you up at your guesthouse or hotel. Kijangs also meet the ferry from the Togeans so you can continue straight on to Manado without stopping in Gorontalo if you wish.
If you're heading to the Togeans, you need to get down to the port, which is easily reached by sitor (local-style motorbike taxi with seat at the front) for 15-20,000 rupiah (the trip takes about 20 minutes). At time of writing, the Tuna Tomini departed Gorontalo on Tuesday and Friday at 17:00, arriving in Wakai at 06:00 the next morning. It continues on to Ampana in Central Sulawesi, departing Wakai at 07:00 and arriving at Ampana at 13:00.
In the reverse direction, the Tuna Tomini leaves Ampana on Monday and Thursday, leaving Ampana at 10:00 and arriving at Wakai at 16:00 and then after a short wait, continuing to Gorontalo, arriving there at 06:00 the next morning. Either way the economy fare is 63,000 rupiah for an adult and 40,000 rupiah for a child. Business class is 89,000 rupiah and 53,000 rupiah respectively.
In practice the boat service tends to run a bit later -- our boat didn't pull out from Gorontalo until after 19:00 for example and a delayed departure will affect arrival times in Wakai and Ampana. Don't plan any tight connection times around ferry timetables in the Togeans.
Tickets can be organised on arrival at the port, but if you want a cabin (there are only four) you need to book these ASAP -- either through your accommodation or get to the pier quite early to try and nego your way into one. You'll need to book the whole cabin, which goes for an additional 400,000 rupiah. In practice, "business class" (this isn't Emirates, so don't get excited), which offers a soft partly reclining seat, is adequate for most, though those travelling with kids may prefer to aim for a cabin.
For those wanting to skip the Togeans but still head south, there is an overnight every other day ferry service between Gorontalo and Pagimana in Central Sulawesi.