Is this because you found a cheap scanner that only scans up to 600dpi? If so, don't buy it. That's crap. I've never had a scanner that couldn't do at least 1200dpi. A scanner with high dpi ranges is a sign of a quality scanner. Something that is cheap and gives you very few options is most likely going to be bad quality.
Even if you don't use 1200dpi all the time, it's still a better idea, because it allows you to make images twice as big, including photos. It's better to have something too big and be able to make it smaller resolution, than to have something with not enough resolution.