I thinking of buying 04 S80 t6 , but timing belt has me freaked out seeing as how car has 105000 miles. I have no idea if belt has ever been changed. Is there way to inspect belt, and average cost to have done?

 

At 105K the timing belt is just now due. No real reason to think it has already been done unless there is a sticker or some other kind of note under the hood indicating it has been. Pricing can vary significantly from one market to another and from independent mechanic to dealer. There are other components that should be changed at the same time like the idler and tensioner and those are included in most kits. Call the nearest dealer and ask them. They'll likely have a price right off the top of their head. Use that price as your worst case.