Most cost effective and timely way to eliminate Fungust Gnats in small collection?

[itzi]

I currently have a few orchids growing inside, 7 to be exact. Recently while doing my morning inspection I noticed some little black insects flying around, and after taking a closer look through my phone camera, saw that they are fungus gnats. I've never had this problem before, so I did some reading here and on various sites and know of a few solutions; Bacteria strains, Ping plants, Mosquito dunks, etc. I just want to know which one of these would be affordable, fast, and not overkill for my small collection. I also will now be letting things dry out a little more... Thanks

My plants, for reference: