If you are thinking about moving to Lisbon or just visit it, or even go in Erasmus , you should first know the prices of the city.
Let´s start with the prices of the houses , if you want the rent a house ,of course it will depend of the area but if you choose a normal area not very far from the center a house with 2 bedrooms it cost between 600 and 1000 euros depending on the state of conservation , the location ,etc…
If you prefer a hotel you can stay in a 4 stars hotel for 60 to 80 euros a night , but also have many hostels in town that are cheaper .
You can have a meal for 10 euros or less in a cheap restaurant , but if you want to have a good dinner you can paid for more than 50 euros for person. At the supermarket you can eat and drink for 200 euros per month
The transports in the town are good and cheap , the metro ticket costs 0,80 , the taxis are also cheap the ride starts with 2,50 euros.
The Lisbon´s night is also cheap , a beer in a "tasca" (typical restaurant that at night is open through the night) costs no more than 1,50 normally it only costs 1 euro , but if you buy beer In a shop it is much more cheap ,in a bar might be a little more expensive but not much, the entrance at a disco it costs between 12 to 20 euros for the guys ,for the girls nothing to 12 euros ,always with drinks included.

Clothing and accessories is not so much cheaper than the rest of Europe but is still cheaper than the rest of Europe
In case of you want to be permanently and need a car do not buy it in Portugal nor with a Portuguese registration because the taxes are very high you can paid the double for a car in Portugal instead of buy in UK for example.
With 1000 euros per month you can live in Lisbon but it will not have much money in the end of the month or any .
The inflation rate do not pass over 2 % and this year ,2009, will be almost 0 .

Check the cost of living in Barcelona and the PSI 20 Euronext Lisbon