Are drugstore setting sprays as good as prestige ones?

For many users, yes. Milani Make It Last and L'Oréal Infallible 3-Second routinely show up in side-by-side comparisons as legitimate alternatives to Urban Decay and Charlotte Tilbury. The trade-offs are typically scent (the L'Oréal is widely compared to hairspray) and finish nuance rather than raw wear time.