Feel free to disagree, but I think 75-90 dollars per person is expensive, especially since most of the trip is in a bus. Busquebus fares are much higher, the boat direct to Montevideo is about 250 USD round-trip, which is about triple the per-mile rate for ferries in the Seattle area where we are moving. Its far more than the cost of the per mile rate for ferries I've taken in other parts of Latin America. One example, the Puntarenas ferries to the Nicoya Peninsula in Costa Rica are $1.70 per person 1-way, those trips are 12 to 15 miles.

Another note about Busquebus, don't bother paying extra for a higher class of service, the snacks and drinks they offer are miserable, you're better off bringing your own water or soft drinks.