DIY? -- Can I approach equal or better quality - for less if I DIY with the likes of with neo or dh cable or other with WG or other connectors... Is it worth the effort to DIY at budget I have set?
No. Not even close. I know one guy with 30 years building DIY cables trying all the hot schemes who every time he showed me one I had something in my used cable drawer that we BOTH agreed sounded better and cost less than he spent on parts. Waste. Of. Time.
Synergistic Research - considering - but I see none in the <$500 range...
A used SR Master Coupler is under $400 and a darn fine power cord. A used Blue can usually be found for $500 or less. Synergistic is so consistent quality wise you can be safe going with any model in your price range, and generally the newer the better. If you find one with Active Shielding those are a great choice because they'll sound good stock and can be upgraded with better caps and diodes in the wall wart by Michael Stallone for a huge increase in performance for something like $50-75.