Well... for starters, you could have the wedding at your local parish church, limiting the expenses of venue rental (and maybe achieving some other economies of scope). If you have an extended network of friends and relatives in the area, they could assist with food preparation instead of hiring caterers. Some guests and relatives may attend the service with their own family and children, bumping the attendance numbers, but skip the reception or send the kids home. Coming in under $100/head should then be easily doable.

Of course this pattern is probably well-correlated with the "goes to church regularly" set and may indicate a level of serious commitment to marriage as "'til death do us part", to say nothing of other demographic differentiation.