I did make bids as low as $0.02 or $0.03. And it depends on what you define as "won." I'm going for the long haul and just want some representation in the AMS ad space. But, like with Google AdWords, I'm not looking to "win" bids. Played that game and it cost me dearly with no results.
Admittedly, it is difficult to find the sweet spot where your ad investments, on AMS or elsewhere, bring the optimal ROI. It does require some experimentation.
What's even more difficult with AMS is that your ad could generate some Kindle Unlimited or Kindle Online Lending Library (KU/KOLL) reads, but those don't show up in your AMS ad sales results. And you have to be enrolled in KDP Select to get those KU/KOLL royalties.