IMHO go with a used Audience Adept Response AR2/AR6 or a Shunyata Hydra rather than multiple single outlet plug-ins. I have seen Hydras as low as $400 - $800 on the used market.
Smaller plug-in AC Purifiers -- Shunyata, iFi, Puron...something else? What do you like?
I like the Shunyata Venom Defender. It does a good job of reducing noise in my outlets.
I'm wondering if others have tried similar, plug in products — such as the Puron Power Filter or the iFi AC Purifier or something else.