How long is a piece of string...... I could name many under $25 but many would be of no use to the average Joe because they are too purpose specific. It gets even harder when one has no idea if we are talking any light or only those that don't need lithiums. As for what's desirable that's always a personal choice depending on many things including what you already have.
However just going with lights that can live on primaries alone and which are terrific general purpose lights I'd say -
there have been a few threads on this topic and you'll probably find a lot of helpful responses if you search the forums a bit.
$10 seems to be where the quality and usability of lights really drop off. a lot of great lights right around $10-13. hardly any under $10. consensus on the best $10 light seems to be the Sipik SK68 and clones. my personal favorite is the $11 Trustfire F20 from Manafont.
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I could name many under $25 but many would be of no use to the average Joe because they are too purpose specific. It gets even harder when one has no idea if we are talking any light or only those that don't need lithiums. As for what's desirable that's always a personal choice depending on many things including what you already have.