We are planning on taking the AVE train late September- Barcelona to Madrid. Do tickets need to be purchased in advance? Does the price fluctuate with demand?
You may save some money if you purchase your train tickets in advance but keep in mind that discounted tickets
come with restrictions & may be nonrefundable & unchangeable.
Check Spain's Railway website for more information:http://www.renfe.com
'Does the price fluctuate with demand?' - Advance purchase discounted tickets only go up in price (or disappear completely) as the travel date approaches.
There are several guides on RENFE and advance ticket purchase available with a google.
And if your credit card doesn't work, use PayPal.
It's much cheaper to purchase an AVE ticket in advance. It probably won't sell out. I believe you can begin to purchase tickets at 62 days out.