There aren't many detached houses in north of Brisbane for 500K anymore. If you're open to a duplex or a townhouse there are plenty of options.
The lowest price currently for a detached house close to your budget is $550K near Pumicestone State school and the Christian school, but most are at least $600K. I've lived here for almost a year in The Reserve estate and would recommend the area for families. Neighbours are friendly and we can walk to the playground, shops and restaurants nearby.