Hi Lisa,
I would recommend to refer to Figure 7-8 from the PMBOK Guide to better understand the difference between the two. From there you can see that cost estimates can be derived for each activity, and (by cost aggregation) work package. When you sum up work package cost estimates and contingency reserves (which are also a form of cost estimates), you get the cost baseline. This plus the management reserves provide you with the project budget.
Does that help you clarifying the difference between the two concepts?
Gabriella