def get_main():
    return [1, 2, 3]

def get_values():
    return [
        {'price': 10, 'main': 1, 'field': 1},
        {'price': 20, 'main': 2, 'field': 2},
        {'price': 30, 'main': 3, 'field': 3}
    ]

def get_fields():
    return [
        {'id': 1, 'name': 'orange'},
        {'id': 2, 'name': 'apple'},
        {'id': 3, 'name': 'tomato'}
    ]

def map_main_values_fields(main, values, fields):
    data = []
    for i in main:
        v = {}
        for value in values:
            if value['main'] == i:
                for field in fields:
                    if field['id'] == value['field']:
                        v[field['name']] = value['price']
                        v['main'] = value['main']

        data.append(v)
    return data

for i in map_main_values_fields(get_main(), get_values(), get_fields()):
    print(i)