When entering an item in order entry the incorrect price is being used.
Sage 300 has robust pricing functionality and is highly configurable. Go to Inventory Control -> I/C Items and Prince Lists -> Item Pricing. Enter in the item number and open the price list for the item that has the incorrect pricing. Check the Sale Starts date and the Sale Ends date fields. If the Sale Starts is filled in but Sale Ends is not filled in then the item may be in perpetual sale. If that's the case then the sale price will override other pricing. Remove the Sale Starts date or enter in a Sale Ends date to resolve the issue.