Welcome from Michigan !
Any year Dog is a great bike .
05 and up Bigdog went to several custom parts. You might ask if it has had EHC replaced and if so what was used. Try to ride it and see it shifts smooth. These years can be (not always) a little more prone/costly for repairs . After repaired done properly your gold.
04 Transition year. Has electronics/hand controls that are custom . Common transmission/primary still. (Last year)
03(first year for the Chopper model)
Use a simple EHC and common harley type hand controls/switches.
My think list.
Try to find/buy bike as complete to end goal as possible.
Condition, most of these are well taken care of, you don't need to get into a project to get your hands on one.
You probably need to like the paint scheme. Not to cost effective to change unless your connected or talented .
Do I want a sissy bar . These bikes require a custom bar and factory rear fender struts prepped for a sissy bar .. Bike without bar probably does not have the struts that accept a sissy bar. There isn't much available to add a after market sissy bar mount and isn't as clean as the oem strut design. None of it is cheap . If needed you can get oem struts with sissybar prep from Bigdogpartsking . They have bars too. Around 1k for both total.
Exhaust, do I like ? something you might want to consider .. 700-1k
Two up seat ? Around 700.
Location .. fetching it adds up .
These are factors that can have a impact on the real total price.