Terrible undergraduate transcripts. Everything else is good. Is it still worth applying to a Ph.D program in economics in a top 30 U.S. university?
Broadly speaking, your more recent work will matter far more than your past work.  You'll see this as a common theme in the many answers already on Academia SE that relate to this subject.

However, as someone who has been through the economics PhD application process, and knows quite a bit about it, I think you need to temper your "top 30" program cutoff.  To get into top-30 programs you'll often be competing against students who did as well as you in later work, got perfect scores on the GRE quant, AND didn't have problems in past work.  

If your math, at a bare minimum covers differential calculus and real analysis, then given the other things you've said I think you might stand a chance at top-30 programs, especially if your private sector job involved any research with your name on it, even if its just an acknowledgment.  So yes, it's worth applying, but I wouldn't suggest setting your expectations on that range.