Best cheap and widely-available option (IMO) is compact fluorescent blacklight. Second best is UV LED fixture in whichever form factor works best for your application. The USB mini Entolight is a good choice if it’s in your budget, as it can be powered from the wall or USB battery pack: https://entoquip.com/usb/
see also previous threads:
https://forum.inaturalist.org/t/light-traps-for-moths-with-limited-power-sources/12028
https://forum.inaturalist.org/t/attracting-moths-with-light-source-abroad/33306
https://forum.inaturalist.org/t/light-setups-for-mothing/48231
https://forum.inaturalist.org/t/mercury-vapor-light-for-mothing/26716