Insurance is a fixed cost and is a very important consideration whether you are buying an aircraft or even just renting.  There are many factors that are considered in an insurance quote from pilot experience to aircraft type.  Insurance cost is definitely a necessary piece of information to help in the decision to purchase a particular aircraft since the cost may have an impact if that additional cost could put the aircraft you were considering out of the range of your budget.  An insurance quote should be requested early on in the purchase planning process.