I order from china via ali express. I've had good luck with RideNow (36g) at $6/tube, Newboler (28g) being my favorite at $3.50/tube with the caveat that the plastic valve stems can become brittle in the cold weather, and I recently purchased a brand called OFFBONDAGE (39g) on some flash sale for $2/tube. They look good, but have yet to install. Seems the normal price is a bit more expensive.