Minimum Order Size for an Average Price

A shop sells widgets such that in an order, it sells P10.00 per widget for the first 100 widgets, P8.00 pesos per widget for each widget exceeding the 100th up to the 500th, and P6.00 pesos per widget for each widget exceeding the 500th. What is the smallest number of widgets that can be in a single order from the shop so that the average price per widget is at most P6.50?