I really like the NAAA Evaluator software that an $18 per year subscription to on-line trade-a-plane get's you. It allows you to enter each piece of avionics as well as the normal stuff for a very accurate (conservative) value. Matter of fact...I am a bank credit administrator, and our bank subscribes and uses it in our aircraft financing as our appraisal tool. You may have to go a bit higher, but it's a great bargaining tool. For that price, you get to value something like 3 planes per day....you might consider it.
