Not only does the material chosen for your windows and door frames affect the cost, but also the types of glass, gas fill, window finish, fitting and locking mechanisms, etc.
In turn these affect the 'U'-value and energy efficiency performance of the window and door. uPVC is often chosen for its utilitarian and reduced maintenance (no painting) characteristics. But softwood may be treated to achieve the same result. Likewise modified woods, like 'Acoya' r 'Thermowood' which are exceedingly durable. Hardwoods tend to be very expensive, but aluminium faced softwoods can be even more so.
Since there are thousands of window types and specification combinations, this is a very important consideration to be discussed with you timber frame supplier at the earliest possible stage.
Typically, windows and doors may cost more than your basic structural timber frame 'kit'.