Fletcher doesn't make the RNC, he sells it along with lots of other gear.
The Aphex Compellor is a good suggestion, I own one and like it. The Compellor is very easy to overuse however, so care must be taken with it. Quite invisible leveling though.
Other than the Compellor and RNC (which I personally have not used), you do have to get into the $2,000 plus range, as Fletcher said. I have a Manley VariMu which works well on the mix buss.
Another option is to use a compressor and limiter in series. Like use an analog compressor and then route that through a good clean plugin limiter. Don't limit by more than a couple dB though.
I think you'll find it to be one of the most highly praised peice of inexpesive gear in ANY category......bar none.
Harvey Gerst has 18 of them in his Indian Trail Studio.
It aint' just because they're cheap.
Also take a look at Mercenary Audio's main web page and look at the list of manufacturers.......it ain't Musician's Friend.
You wont see Nady, Samson or Behringer in the list.
The only thing I could even afford from there are the RNC an price point Funk Logic stuff .
The RNC is recomended by many who have and can afford MUCH more expensive gear..... is this only in the name of a not so clever marketing conspiracy......I doubt it.