At 11am, we made it to Los Manos. There was no fee for leaving Honduras. The process was sorted within 10 minutes. However, the same cannot be said for Nicaragua side, which took a further 2 hours of 'too many cooks' and slow processing workers. There was no permit fee for the vehicle, but it did require a fumigation spray ($5usd) and insurance ($12usd). There's also a tourist fee of $10usd pp with an additional overland fee of $2usd pp. We had read about this before we came and all fees came with an official receipt for doubts. There is also a $1usd fee, which we don't know what this is for, but everything seemed legitimate (again an official receipt was given, plus locals were paying it too).
We then made the 30 minute journey to Somoto and managed to get on an afternoon tour of the Rio Coco for $20usd pp including hiking along the rim of the canyon and then swimming through the river, jumping off cliff edges and scrambling over rocks, with a boat ride to finish. We had a good time and cooling off from the heat in itself was worth the money.
After eating dinner over looking the Nicaragua countryside, we drove the 3hours along highway 1 to the Managua airport (the international one - 12km east of Managua). We booked with La Costena for the 6am flight to Big Corn the next day, but we were unable to park up in the airport parking area in front of the terminal that night and had to come back at 4am. At 150 cord (£4GBP/$6USD ish per day) it's worth the security. Best Western Hotel across the way provides free parking, but only if you're a guest...or the security guard will usher you to move along.