For the Philips Viva Collection HD9721/21 air fryer model with Twin TurboStar, Amazon's Black Friday 2019 pricing seems to be the cheapest. Google indicates other retailers having it on sale for circa $220 making this a significant saving.
I personally am a huge fan of the Philips air fryers and find them to be fantastic for cooking various things but primarily frozen chips/chicken tenders/etc… if you're more adventurous there's a Youtube channel (and numerous Facebook groups/communities) dedicated to simple recipes using an air fryer.
Is this big enough for a family of 4?