Many challenges can come along with the intent to evaluate your program. Evaluations can require substantial resources, including staff, funding, and time.
Identify and involve an evaluator at the beginning. Early discussions with your evaluator can help you avoid expensive mistakes over both the short and long terms.
If possible, talk to several developers who have gone through this process to get their insights. You may want to ask about how much the evaluation costs, both in terms of dollars needed to hire external staff and internal resources used to support the evaluation.