Audio enhancer

The cheapest automated equalizer plugin I know of is Hornet thirty-one …
ThirtyOne, spectrum analyzer and graphic equalizer with auto settings - HoRNet Plugins (~$10)

There are many free multi-band compression plugins …

Mastered FM radio compressor preset - #7 by Trebor (sounds like FM radio)

There’s a free plugin called La Petite excite … [Free] [VST/AU plugin] La Petite Excite
It’s billed as an exciter, but it’s actually a 2-band expander: boosting the bass (low) and treble (high).

(expansion is the opposite of compression).