We've stayed at Macdonnell Ranges (Big 4) and it is really excellent, but of course not cheap. We've heard good reports from friends about G'day Mate across the road from Big 4.
We've also stayed at Wintersun at the north end of town. It's quite okay as caravan parks go, all the usual amenities, friendly staff, but the neighbours living adjacent to the park are very noisy at night - fights, barking dogs, roosters etc. We were camped close to the back fence, so maybe okay if you're up in the middle of the park area.