As to cost differences, trust me that there are major differences if you really look. I could post specific info here and give you
Albeit these websites method of operations is less than ethical in the travel industry. For sure though, this is America. If someone doesn't place any value on their time, and wants to spend hours on the internet searching different sites; then that certainly is their prerogative.
Most Travel Agents are in the business because it is their passion. They enjoy traveling themselves, and they enjoy talking about travel and helping others plan their travel. They think, breath, and live travel. They basically are on call 24hours. How often have you been somewhere and met a Travel Agent? When you asked about travel did they say "Here's my card, make an appointment and come in and talk."? No, they gave you free advice. It's a pity so many don't recognize the dedication, professionalism, expertise,knowledge, and hard work that a Travel Agent does. A Travel Agent that has been on 68 cruises has been there, done it, seen it; so they can advise you on what cruise line, ship, itinerary, and time to travel is best for you. They have all the up-to-date knowledge on what is happening with ship refurbishments, itinerary changes, new ships, hot new destinations, and cruise line policy changes. They will have insight on things to know, do, and see. They will provide a lot of those "I didn't know that, or think of that" ideas. They have titles and initials behind their names that stand for hours or years of training. And their training doesn't stop there. It continues almost daily in the form of supplier emails, webinars, reading travel industry newspapers and magazines, taking on line specialist courses, attending conventions, conferences, ship inspections and trade shows. Many do it with a lot of out-of-pocket expense, all because they are dedicated to learning more to help you. Many agents still offer their services at no additional charge. Many people bulk at those that do charge. But why shouldn't they? Their expertise is just as valuable as a lawyers or accountants, and people willingly had money over to them.
Next to homes and cars, a vacation can be the next most important purchase you will make. But yet; so many are so willing to put their vacation in the hands of a computer.
Just because someone has a computer though does not make them a Travel Agent. No more than knowing how to put a band-aid on your knee makes you a Doctor.