One of the best under 500 bucks! - Vortex StrikeFire II 1x30mm 4 MOA Reflex Red Dot Sight

The reliability, lifetime no questions asked warranty and durability make this an easy choice for anyone on a budget. It does lack the auto on from movement function so using it in a home defense situation or any situation where you’re not necessarily ready for a threat could be an issue. Using it for practice, competitive, hunting shouldn’t be any issue at all. Vortex’s warranty is second to none. Light it on fire, beat it with a hammer? No problem it’s covered.