DNA Day is April 25th. The DNA testing companies usually hold DNA test kit sales to commemorate.
Ancestry DNA is having a sale on DNA kits through Sunday, April 29th. The price is $59 plus shipping (about $10 for the first kit, about $5 for additional kits). I often suggest to buy kits on Amazon to avoid shipping costs, but as of April 20th the Amazon price was still $99. Note that this sale ends midnight Eastern time, in case you are shopping last-minute.
FamilyTreeDNA has sales on its many test kit options. The autosomal DNA kit is on sale for $49. This sale ends April 28th.
Test kits at MyHeritage are $69, through April 26th.
Test kits at 23andMe are 30% off, through April 25th.