Final answer:
The best comparison to isolate the impact of changes in input and output prices on performance is between the flexible budget and actual results, which takes into account the actual costs and revenues for a given level of output.
Step-by-step explanation:
The comparison that best isolates the impact of changes in prices of inputs and outputs on performance is between the flexible budget and actual results (Option C). A flexible budget adjusts for changes in the volume of activity and can be used to compare the actual costs incurred during a period. This comparison allows a business to see the effects of actual prices and efficiencies compared to what would have been expected for the actual level of output. By doing so, the flexible budget takes into account the changes in costs and revenues that arise due to fluctuations in market prices of inputs and outputs.
A static planning budget is set at the beginning of a period and doesn't change, making it less useful for this purpose. The master budget is a comprehensive financial plan, but it does not specifically isolate the changes due to input and output prices like a flexible budget versus actual results comparison does.