I have a Canon 5000F scanner, which scans at 2400x 4800 without interpolation. This gives a good result (better than scanning a good photo). However, if you do this regularly, I would buy a film scanner.
I just bought the Epson Perfection 3170 Photo scanner. Very good quality. Takes up to 2-1/4 square negs and slides. The only problem I found with it was, if the negs/slides are over exposed it can't find them. I also have a dedicated film scanner (Primefilm 1800) which I found if the Epson can't scan the Primefilm can.