Ok,, do any openly state if they have closely regulated voltage?

If they have voltage regulation (or possibly automatic voltage regulation)
they will feature it in their advertising copy, as it is an important and
expensive feature. If they don't mention it, they don't have it.
Sadly, it will probably cost twice as much as an unregulated genny, but you
get other good features as well; such as low noise, etc.
If price is a problem, you might get lucky with a used one. Last year I
bought a small used regulated Kawasaki with only 20 hours on it for $350; it
was about $1,000 new, but apparently the market for used Kawasakis is not
good. (Or you might get one with 1000 hours without an oil change; you have
to be careful.)