Go through your results for flights to Rock Springs in the USA with Netflights.
If these flights are too expensive, try searching for a different time of year. It's likely that prices for both flights and accommodation So if your dates are flexible, consider looking at different times of year.
But if you're struggling to find flights to Rock Springs that work for you, try looking at other airports in the USA.
You can also broaden your search by looking at more than one departure airport. Have a look around – you might be able to save by flying from a different airport or city.