I don’t really know what to say about the costs/ who to manage it, but I think something like this would be simple and affordable:
An oatmeal bar for breakfasts
A soup and sandwich bar for lunches
A burrito/taco bar and one other nice meal for dinners

I like that idea – pasta and salad bar. Add in late night deserts, coffee, tea, cream and sugar, plus lemonade/ iced mint tea or something cooling and refreshing for the daytime. If people wanted to contribute in small ways to meals, we could send the menu out ahead of time and let them know they could bring extra items for snacking or to accompany courses – things like pickles, olives, extra cheese, popcorn, chips, hemp seeds, etc… having the menu out ahead of time also would allow people to plan on bringing certain items they may want/ need because of dietary restrictions/ preferences.