Maybe the battery size is just not as popular, but I’d like the extra capacity even if everything else about the flashlight is the same as a regular 18650 light. I know that Convoys are a no-brainer for quality in the budget 18650 category. Anything comparable in 26650 lights?
Is it still available for <$20? DX and eBay vendors have the F13 for >$20. FWIW in the very big F13 Group Buy(s) I think that the price was in the range of $10-15.
FWIW if you break into the $25 range there is the Supfire L5 with it’s momentary side switch. I can’t speak to that one, but might as well mention it. [Missed opportunities: The Yezl Y3 was once available at $25/unit. The Keygos M10 was an early budget 26650 light which was probably actually inside your $20 pricerange at various points but is no longer available afaik.]
a LED swap to a good tint is a start, then a driver upgrade really helps it. (like a Nanjq 105c Q-Lite.) and with a 4500mah 26650 the run time is great.
I ordered two ThorFire JM07's from Amazon when they had them for $9.99 shipped, now no longer. I love single cell 26650 lights and got a ton of them. It is a challenge to find one under $20 though, specially a good one in stock form. The F13 and it's clones have always been a great deal though.
One of my favorites (but over the price limit) is the K2 (Solarstorm and FandyFire) - quality w/SS bezel, very stable tailstander. In Stock form, not sure how good it is, but modded up it's real nice.