U.S. Agencies can vary greatly. You can find rates from freelancers in the $50s, agencies usually begin around $125, and large design firms can charge up to $300 an hour. It’s a pretty wide range to work within.
You may have some luck looking at portfolios and hiring a designer directly. This will always be cheaper than the agency route.
Or go to a template site, and have someone on the team make adjustments as necessary. This is your cheapest route.