Last time I visited Porto, I've stayed in this hotel. It's a simple and clean hotel inside Porto, with minimal services.
The rooms are clean, but small and there is no restaurant in the hotel. You can eat a frozen pizza, by buying it at the reception and putting it on the microwave hoven that is available in the hotel atrium.
It's not near the city centre and you will need transportation (probably taxi) to reach the city center.
However, it's probably virtually impossible to arrange a cheaper hotel with this conditions (clean, tidy and quiet) in Porto.
Private car parking spaces are available if you pay a fee but you have an excellent parking lot in front of the hotel for free.
