What I have, and it works quite well, is a Korg MA-1 digital metronome. Under $20 where I got mine. It can be set for a variety of beats and rhythms, at a tempo from 30 to 252 BPM. It has a small speaker, but also a volume control and headphone jack. When I do use it, I use it with a single ear bud in one ear so I can still hear my bass with the other.
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