I think the difficulty for the foreigner not speak Portuguese, but adapt to the system that is quite different, particularly to avoid Monte Carlo because their rooms are small and old, but women are beautiful, this way of Thermas no better than 4x4 today, cost and benefit very attractive, but also pay attention on the homes of the Avenida Rio Branco, are good, there are many girls in the level of Thermas these places, for $ 70 to $ 130 against $ 250 to $ 520 of the 4x4.
Another difficulty is the taxitas, bad service, too expensive, there is always a tricky this way, better to use the subway between the hours 10 am to 11 am and 14 pm to 15 pm and 20 pm to 23 pm. Preferably the places near the metro.
With little money, you also have fun, there are places reasonably clean in the center of Rio, better than the Vila Mimosa, from $ 20 per 20 minutes up to $ 80 per hour. Just do not offer comfort. Always around the Avenida Rio Branco.