I vaguely remember advice on affordable hotels in Buenos Aires a month of two ago. Have you tried "search" yet? It might have been to a response in the UA forum, rather than this one.

I have taken the ferry to Uruguay as a day trip. The town at which you land is quiet, with nothing in particular to do. You spend several hours on the ferry to get there and return.

If you have never been to Buenos Aires, there are more interesting things to do. There are organized city tours, that take you to sites made famous by Evita, to the barrio where there is tango dancing in the square, and to the barrio with vividly painted houses. There are two well known cemeteries. One houses Eva Peron's body; the other that of Juan Peron. Burial sites are ornate and expensive, costing as much as a few hundred thousand dollars. And if you have stamina, go to a tango show one of the two nights you are there.