A store price changes with the country of whoever looks. To track the price seen in the United States, the address has to come out of there, and it has to be the same across days. Changing address between readings changes the result without the price having changed.
How many to buy
One address per market already reads the price. More addresses come in when the store limits how many lookups one IP can make. Start with one, measure how many readings it handles per hour, and only then grow.
Dedicated avoids the other customers on the same address spending that quota for you.