Tickets are the least variable expense for a WDW vacation. They are the same price whether you stay off site, or in a deluxe villa.
With WDW vacations, you can sometimes get 'a deal', like free dining, or kids play free, or buy 4 get three free, but usually you can get the best deals, driving to Orlando, staying off site in a condo, cooking some of your meals, or staying off site.
The amount you spend can vary greatly. Figure out the cost, at today's prices, for the vacation you want to take. Remember, if you have a budget, your grocery amount for the number of days you travel, can go toward your vacation dining or meals in your condo.
Set a date for when you would like to travel. Divide the amount by the number of months and divide appropriately.
Remember to add in some souvenir money, if it is your first trip as well as money for snacks, etc, in the parks each day.
Have fun planning and saving! There are a lot of threads here, that can help you with both!