While I don't know for certain, I'm pretty sure that if you want to get married on WDW property, you have to go through their coordinators. Also, I would guess that they have a minimum expenditure requirement, but I know that they offer a variety of services. So maybe they'll have something that fits into your budget (e.g., small ceremony at one of the resorts and cake cutting ceremony, etc.).
If even the minimum fees are out of your budget, I have some suggestions for having your wedding in the WDW area. (I am a wedding planner when I'm not an attorney!) First, you could have a small ceremony at a local church during the week. Many churches just charge a small fee if you are a non-member (maybe $500 plus a cash "gift" for the minister). If you have a minister in mind, he might be able to help you find a church and arrange for you to pay a reduced fee. If you wanted a small reception, you could contact one of the local supermarkets and have them make you a simple cake, which you could serve with sparkling grape juice, champagne or even just punch. (FYI, many grocery stores now offer bridal bouquets, too.) The church might let you have the reception in one of their reception, Sunday School or recreation facilities for another small fee (although there would be no alcohol allowed, I suspect).
Or, if you don't think you can find a church (or don't want to get married in one), you might contact a WDW area civic club (Lions' Club, Rotary, Women's Club, etc.). If they have a facility, they might let you rent it out for a small fee, and you could have your reception and ceremony there. The same thing goes for a community center, art museum, or small restaurant that has a private room (or is only open for dinner and would let you get married during the day).
Really, there are endless possibilities, and you will be surprised with what you can do on a small budget (and how great you can make it look).
