Yes, it is all overwhelming, when you first start!
The question of how much it will cost can vary GREATLY! It depends on so much. When my husband and I began planning our trip (with little to know knowledge) we priced it at $3500. Not that I have learned some things, I have gotten it doen to $1500.
I think the Internet is your best bet. Prices and things change at Disney weekly, and no book will be up to date enough. Though I DO reccomment Rita Aero's Disney Guide to have while you are there, it is easy to follow and gives a good ratings/reviews of all the restaurants and attractions.
I would start with making up your own budget based on what you can realistically afford. Then determine what time of year is best for you. Yes, Spring break is one of the busiest, most expensive times. If you are just wanting to go when school is out, I would say do the summer instead of spring break. It will be hotter, but prices are better, park hours are longer and crowds will not be as bad (though still busy) The best times to go as far as crowds and getting discounts are. Here is a really good chart that tells about crowd size/weather:
http://www.destinationdisney.com/guide/page/crowdchart.html
Staying offsite will definitely save you money on larger accomodations. But you will need to travel to and from WDW and that would require having a car. If you are driving down, that is great, but if you are flying you will need to rent a car and that will be add more expense. There are many who swear they would never stay offsite. It is a personal choice. My first Disney trip we stayed offsite and I had a blast. Look at it this way: if you have never been, you will not know what you are missing! In my opinion, you will get more for you rmoney offsite, but you will loose some of the experience that Disney hotels offer (though at a price). If you stay offsite, you can park your car at a theme park, and use Disney transportation the whol day to get to places within WDW. Familiarize yourself with the layout of WDW (It's huge, 49 square miles... the size of San Francisco!). Here is a map:
http://www.wdwinfo.com/wdwinfo/maps/WDW_OVERVIEW_INTL.jpg
Also deciding what type of tickets you will want will be important. You can get one day/one park tickets. If you plan to stay more than 3 days, these are not the best bet. You can get Park Hoppers, which allow you to go from one park to another in the same day. (There are 4 Disney Parks) These come in 4 and 5 day versions. You don't have to use the days consecutively. There are Park Hopper Plusses which come in 5, 6 or 7 days. Days don't have to be used consecutively. Each ticket comes with a number of "Plus" features (2, 3 or 4). Plus features include the water parks or Pleasure Island. People like these because, for example, with the 7 day 4 Plus ticket, you can use it for up to 11 days of Disney fun. Unlimited Park Hoppers (Also known as Length of Stay Passes) are only available only when staying at a Disney resort. You can come and go freely to and Disney attraction your entire stay. There are also Annual Passes for unlimited visist the entire year.
Check out the Ticket grid right here on WDWInfo:
http://www.wdwinfo.com/wdwinfo/tickets.htm
Here's a tip that I think everyone will agree on: don't buy a package. You will end up paying more for things your probably don't need. Its always cheaper to book hotel and park tickets seperate than to buy a package.
The parent site to these message boards,
www.wdwinfo.com is one of the most comprehensive information sites on the web!