I took a day trip here after staying in Buenos Aires for two weeks. It was a nice little break. I think the ferry dropped us off at around 9:00 and the returning ferry back to BA left around 20:00 and it was only about $40 US. It was very beautiful, but I was getting bored the last hour or two and ready to go back to BA.

I would definitely recommend it though! I had a few hours of fun sightseeing and learning all the history of that area of Uruguay!