The Sale Price field is an alternate selling price which may be used instead of the Base Price.
If an item is marked On Sale, the Sale Price is used instead of the Base Price.
However, if a lower price is available through a valid Price Table, that price is used instead of the Sale or Base Price.
When entering new Inventory database records, the default setting for Sale Price is 10% less than Base Price.
See:
Inventory Database - Main Screen - Selling Prices
Inventory Database - Main Screen Fields