Chris, same for me, but I knew at Xmas. I doubt you’ll find an hotel in Barcelona unless you are very monied. We are staying it Sitges about an hour away South of Barcelona, although you could try Blanes to the North (both holiday resorts).
Having a 3-day ticket with parking we are in Car Park C, the entrance to which is near the IBIS hotel next to the circuit at Polígono Industrial Can Catalá Calle Can Gordi, 1, 08400 Granollers, Barcelona, Spain. We’ve hired a car, but if you trawl this site and the circuit’s website and google, you’ll find you can get there by train with about 20-30 minutes walk from the station.