1. Sail in the off season when the prices are a bit less if you can. We love September the most
2. I buy discounted Target cards on Cardpool and then turn around and purchase Disney cards at full value for less. For example, I just bought 150.00 worth of Target gift cards for 142.50. Then I purchased $150.00 in Disney cards for $142.50 at Target.com and did not pay for shipping. Every little bit adds up. I put all of my Disney gift cards onto 1 card up to $1,000.00 each and use those to put on my onboard account to pay for excursions, drinks, etc. Anything that is not used goes back onto the GC. Sometimes I just go into Target and buy a few hundred dollars worth at a time for the discount. But if I have time, I buy them via Cardpool.
3. We don't have cable so that cuts down about $120.00 a month in useless expenses for us, which I turn around and use to put into my vacation account.
4. I am a TA, so my commissions go back into my travel account as well.
3. The prices change based on category, length of cruise and destination. Also if it is a special cruise (like Star Wars Days at Sea) or such the prices tend to go up.
4. Book either as far ahead as a year or try and get those GT rates closer to the sail date. The IGT, OGT and VGT rates are actually pretty close to opening day prices anyway, but you don't get to choose your cabin. And it is a restricted fare so there are all kinds of rules on those. For example, must be paid in full on booking (as they are usually offered after the PIF date for that sailing), you will get a cabin in any of those areas you selected but you just don't know where on the ship it will be and you don't choose.

But the flip side is that you might end up with a cabin that is a better category than you would have chosen. We did that on our January cruise and we were quite pleased with what we ended up with. So much so, that now we choose that cabin for our cruises. lol
5. Look at your expenses and see if there is anything you can cut out of it.Some friends of mine were Starbucks fans, but then decided to try Dunkin Donuts and have never gone back.

That might be taking it a bit far though if you are a Starbucks kind of person.
It is affordable, you just have to figure out what your family's needs and travel wants are and then go from there. There are some on here that sail in Inside cabins and some that swear by Concierge...and everything in between. Decide what you want and you will do fine!