While some entry-level positions, such as case aide or social work assistant, might be attainable with a Bachelor's degree in social work (BSW) or a related field, the salaries are substantially lower than those of licensed social workers with MSWs. You're also likely to face a smaller job market and fewer advancement opportunities.
In short, it's difficult to give a precise number, as salaries vary greatly by location, experience, and employer. However, expect a considerable pay gap—potentially thousands of dollars annually—compared to someone with an MSW. The difference could easily be 20-40% or more, depending on the specific job and location.