def find_budget_friendly_option(selected_product_details):
    """
    Finds the most budget-friendly option for each category of products.

    Parameters:
    selected_product_details (dict): A dictionary where the keys are product categories and the values are lists of product details. Each product detail is expected to be a dictionary containing a 'price' key.

    Returns:
    dict: A dictionary where the keys are product categories and the values are the most budget-friendly product details for each category.
    """
    budget_friendly_options = {}

    for category, items in selected_product_details.items():
        if isinstance(items, list):
            lowest_price_item = min(items, key=lambda x: x['price'])
        else:
            lowest_price_item = items

        budget_friendly_options[category] = lowest_price_item

    return budget_friendly_options