You can pretty much always find cheap Oko Hi Fibre somewhere, that link looks good though.
It’s the exact same thing as the Halo Fibre-Tech in bikesandboots’ link that got 4.5 stars. IME it seals about as well as Stans (who really knows? Punctures are a bit random) but it lasts better- it’s water based and also water soluble so as long as you don’t let it dry up completely you can re-dilute it with more water. (once it’s dry, it’s dry, though- like water based paint) It’s fairly thick so some people recommend diluting it straight from the bottle, not sure it’s necessary myself.
So it’s cheap to buy and it lasts and it works, can’t see past it. Only downside is you can’t guarantee finding it in a random bike shop and you can’t mix it with stans, which you pretty much CAN guarantee finding.
