Susan, how big is your yard? You need at least 2450 square feet for a stand up reception this size and that is with NO tables other than the serving tables and NO chairs... you have to at least double that to provide seating.
Also, this is way too big a group to serve from a single family kitchen- it would take at least 4 standard kitchens, and that is with experienced cooks (2 per kitchen) and at least 25 (yes twenty five) servers, not counting bartenders, if any.
So if you are having it catered, probably the least expensive is BBQ, but that is not very formal or dressy.
Maybe you need to cut the size of your party? As you see in my article, cooking for over about 100-125 requires a commercial type kitchen and storage.
If you have not yet scheduled the wedding, I urge you to select 1 PM or 7 PM so you can have a tea/dessert type reception, which will cost 1/2 what a meal would cost.