Amazon has their 50% off Sonifresh deal again with coupon code BSWWQHS6
Tried with E series, doubt it works with others as they have other promotions.
Works on multiple items as well.
Got 8 E series replacement for $16.99.
Free shipping on Prime / $25 per Amazon policy.
These are the best E series replacement that are not OEM in my opinion.
Can't beat them at around $2/pc.