Like every time before when we had to cross a body of water (except for that time when we crossed the Magellan Strait in Chile), crossing the Oiapoque was not without hassle: the prices (for a 15 minute trip by canoe or ferry) varied from 20EUR to 200EUR but you never know who can be trusted and who can’t. Even the ferry had no schedule at all! After two days of bargaining we managed to find some guys willing to take us across for 30EUR.
In the end we paid 35EUR because they claimed the bike was heavier. For us, it felt so strange: we were in South America but also in European Union at the same time.