G'day Ang
I use a magellan 315 up here (NT) and it has served me well. Costs around $400-$500 and comes with a cig lighter plug and some computing software. You can plan your trip on your computer and then download it if you want.
No need to spend thousands on a GPS (unless you want to
).
It's still working like new even after being operated outside its maximums of temp and humidity. Even had water running over it and it still works fine. The battery area is sealed with rubber and the rest must be put together pretty well as I wasn't the most gentle operator at times.
Best to just get into the shop and play. I've never used the stored routes - as your flights generally gets changed so often with ATC, your ops dept and weather.
Good luck