Rock the custom fields? You could do this manually or by using a plugin such as magic fields or PODS.
I've never used PODS but I've been eying it for a while and think this may be your best route. You could do something like creating a category called "breakfast" and one called "lunch" then two text fields:
1) Item Name
2) Item Price
then
$pods = new Pod('breakfast');
$pods->findRecords('name ASC', 99);
while ($pods->fetchRecord()) {
echo $pods->get_field('item');
echo $pods->get_field('price');
}
They would then just have to add and remove food items based on month.