I hope this is not too late to be of help... But, you are not charging enough. This is less than 10 dollars per person! They would pay more for a sandwich and an ice tea in any local restaurant. Are you responsible for beverages? This is a cost that can really run away with the budget. If you are using disposable serving ware this is also a cost that can really add up. Especially if they want the “nice” stuff. What about clean up?
The cost of fruit and “finger” veggies has been very high in my area. If you get to the market and find that strawberries are $3.99 per pound and cauliflower is $2.99 per pound, you have just blow away any profit from your labors. Figure on the almost worst case scenario and then rework your numbers. Your clientele sounds like they may be fairly sophisticated, and more realistic about costs then you realize. As caterers we like to offer an attractive price to help with word of mouth advertising. But in this case, I would make sure you have enough in the budget to do the job well, and the quality of your work will speak for you.
Several years ago I catered a similar event for 30 and charged $16 per person, they provided beverages. It was high summer and I had access to fantastic fruit and veggies from the local farmers markets for very reasonable prices. They cheerfully paid.
Just today in the mail, I received an invitation to a fancy finger food event, no host bar, served on disposables, and the “requested donation” was $45.
Good luck Nancy! Hope this helps.