Do I need a $500+ detector or is a Cobra enough?

Specialist communities are pretty blunt about this: cheaper detectors like the Cobra RAD 480i can alert you to radar, but they false-alert frequently on blind-spot monitoring systems and automatic door openers, and lack GPS lockouts to silence known false sources. If you only drive occasionally, a budget unit may be fine; for daily highway commuters, the consensus pushes toward a Uniden R3 or higher.