I saw this one trick before I left reddit. They attached food to an arrow. Fired from one korok to the other. Attached the korok to the attached food. Reversed the food/koroks time to where the original arrow was fired. Try that if you're low on devices

Two fans on a plank with a steering stick are pretty much the most cost-efficient boat you can build. You can try to get creative using a big wheel to make a paddle similar to a steam boat, but in my experience those don't work very well. Maybe a stabilizer could help.