So our Mitsubishi units have these "special" anti-allergy enzyme filters that are about $50 a pair to replace and the recommend replacing them every 2-3 months.

• https://www.mitsubishi-electric.co.nz/shop/item.aspx?item=mac-408ft-e
• https://www.mitsubishielectric.com.au/blog/understanding-your-air-conditioners-filters/

Are these really effective and has anyone found a cheaper alternative?

We clean our filters around twice a year, but these special blue filters aren't supposed to be washed and can only be replaced.