FBinNY 

I think it boils down to opinions about what is correctable. IMO, a 3mm deflection over a span of 90 degrees with a comparatively flexible single wall rim is very correctable.

Of course, we never know all the details, like whether the error was originally much greater and this the best that could be achieved. And of course what's fixable, and how well depends on the skills of the mechanic. Something I, you or someone else can fix may be impossible to someone else. This is especially true with wheel building and alignment, which some degree of "touch" is as important as general skill and knowledge.

FWIW - I post here to help solve problems practically and economically. It's very easy to say "it's a bad part, replace it", but that often entails spending money unnecessarily, and the sin is compounded in things like wheelbuilding where there's a decent likelihood of ending up back in the same place. This is why, I offered a detailed outline of good practices, and suggested the OP loosen all spokes and start anew with this rim. If he takes that advice, the best case is that he saves the cost of new stuff, and maybe learns something. The worst case is that he "wastes" some time refining his skills and improves the odds of doing better next time. IMO- that beats using new parts in practice sessions.

Also note that the OP originally said it's a low end bike and he didn't want to spend much. Wouldn't that argue for making a serious, good faith effort to work with what he has?