Drake summed it up best.
I think you have something slightly confused - it's not outer barrels that people tend to not like, but rather the two peice ones (that wobble and require constant tightening to remedy) or the cheap pot metal ones that aren't very durable. Reinfoced barrels tend to be one solid peice or made from a sturdier metal (such as aluminum or steel) to combat this problem.
And as for reinforcing it yourself...you'd likely be better off in the long run taking the 80 dollar hit for a better barrel. Or buy a used one and save a bit of money. Unless you really really
know what you're doing, most fixes would only be temporary and cure the symptoms rather than the disease, so to speak.
Be thankful you don't live in Canada - airsoft prices are way higher on this side of the border
EDIT: I can't say for sure whether glue would have completely eliminated the barrel flex, but that won't increase the resilience of the barrel or reduce the stress placed on it by the launcher.