According to google the best time to travel domestically in the US is either during spring (late March to late May) or autumn (late September to late October). Since these are the shoulder seasons before and after summer, these months have milder temperatures as well as fewer visitors in the most popular destinations.
But in the warmer areas such as Florida, California and Las Vegas, spring and autumn usually offer the best all round holiday weather.
Is USA expensive to travel?
According to Budget Your Trip, the average cost of a one-week trip to the United States for one person is US$1567. Considering your daily budget, a one-week trip to the US should cost: Low budget: US$550-1000 per person. Mid-range budget: US$1500 per person.