Every different host / orphanage / school will have a different existing arrangement for food. 
Unfortunately, not every volunteer is going to enjoy Kenyan food, or the food normally cooked for the children. Therefore we cannot make a rule that every volunteer pays a certain amount of $$$ a month for food, because many will prefer to choose their own food.
What volunteers on the short summer program are told (on the website and in the handbook) is that it will be cheaper for them to buy food themselves, with their hosts. They should discuss meal arrangements according to the specific existing arrangements.
This means if they have to pay to take their hosts with them to the town to buy food then that is their cost. (It will be cheaper if your hosts literally go through the checkout for you as locals are charged much less than “richer visitors”).
If they wish to pay their hosts to prepare meals like the children have and anything else they may prefer then that is also their cost. A volunteer must pay for the priviledge of having the food prepared for them. If they want to cook their own meals (in a solar cooker or over a fire) then the price would be cheaper.
The problem is that individuality means a general rule cannot be placed.
For longer term volunteers, it is acceptable to pay a fixed amount to cover meals and accommodation, bearing in mind they will probably not always eat the same as the children, may go out to eat, may be invited to a locals house to eat, etc. I believe USD$ 200 per month per volunteer is acceptable (including an extra amount to help with anything the orphanage may need).
Shorter volunteering including the Summer Program, accommodation is free at your host.
AVIF are aware that volunteers have spent a massive amount of money simply travelling to Kenya. It was their choice to come, but it is still a large amount of time and money they have committed to help the children.
AVIF are also aware volunteers will no doubt bring many donated gifts and classroom materials, and will very probably buy more gifts for the children or spend more money on their hosts during the visit.
The point being made here, which may differ from a poor, rural Kenyans view, is that people are always more open to help, if they do not feel obliged. Money has a negative effect on people this way.
Volunteering by its pure nature, is a person offering their help. Unfortunately, where financial donations are involved it is very easy to offend someone by asking for too much.
Volunteers (assuming hosts have bought the food with them and you are not charged “visitor prices”
should only spend around USD25 a week on food.
This is NOT a fixed amount and emphasis must be made on making clear arrangements at the beginning of your volunteering with YOUR host, according to existing arrangements and your own preferences.