600cr/t isn't bad. It depends on how long it takes station-to-station. It could be much worse; you could be trading scrap and biowaste over 200ly!
I ran a similar intra-system route when I first started. My tip would be to head to the frontier and find a pure industrial economy with no extraction or refinery capabilities, then find a nearby refinery economy and trade metals. They are very lucrative and you'll make cash pretty quickly. Use the filters to sort by population size for the industrial economies. This will be a bit fiddly and time-consuming as the galaxy map only allows one filter to be applied at a time to prevent, I think, people finding great routes really easily.
Others, of course, have their own techniques, and I'm sure they will chime in with them!