No, I don't think it sounds outrageous at all!
We looked into having a catered affair in Delaware Park, but as our wedding planner reminded us, you have to rent everything from the ground up. That means; tent(s), floor, chairs, linens, silverware, glassware, lighting, restroom facilities and the like...even more if it rains or is chilly. We quickly realized that was beyond our means. If you have a relative who has a yard big enough to accomodate the number of guests you are planning on, that would be a good alternative and one I would recommend. Even there, you are dealing with a large amount of rentals and insurance, but it would definetely be exactly what you want.
As for caterers, you don't mention what kind of food you want but there would be logistical issues involved too. Obviusly a pig roast or "upscale" barbeque (steaks & seafood) would be easier than having multiple plated courses. You have to consider the quality of the food you will be getting. Food that is prepared offsite must be held and transported before being served and may not be as good as when it was first cooked.
After learning all this, FH and I began to look for a site with both indoor and outdoor features. We looked at Shanghai Reds, Hrry's and the Hoiday In Grand Island. They all have outdoor space that is directly accessible from where your reception is. We wound up booking at Top of the Falls restaurant on goat island. They have 2 patios and since our wedding is after labor day, they can close the restaurant for our wedding. I highly, highly recommend them.
Anyway, sorry this post was so long, but I hope it helped. Good luck in your planning!