The lowest I've seen (and indeed quoted by an FTer) was 0.475p per Avios for part pay, though it does indeed go to around 0.8 fairly readily. I still think that's silly usage since it isn't difficult to get 2p per Avios - or far higher if you are in Asia, USA, South America on particular routes. The one exception is that about once a year BA offer a special deal on part pay, which can get you towards the 1.2p level (still crummy in my book). The key thing being for seating, wine, part pay, hotels, car hire - there is a basement level of somewhere around 0.6p which is where BA presumably is delighted to get the Avios off their books. There are so many better uses for them and the gap between 0.55p and 0.7p, 0.8p is immaterial against this.