Ааа да :) Допълнителната отстъпка е процент от вече намалената цена, а не от първоначалната.

Благодаря.

group_budget = int(input())
season = input()
fishermans = int(input())

spring_price = 3000
summer_price = 4200
autumn_price = 4200
winter_price = 2600

additional_discount = 0.00
trip_price = 0.00

if fishermans <= 6:
    additional_discount += 0.10
elif 7 <= fishermans <= 11:
    additional_discount += 0.15
elif fishermans >= 12:
    additional_discount += 0.25

if season == 'Summer' or season == 'Autumn':
    trip_price = summer_price - (summer_price * additional_discount)
elif season == 'Spring':
    trip_price = spring_price - (spring_price * additional_discount)
elif season == 'Winter':
    trip_price = winter_price - (winter_price * additional_discount)

if season != 'Autumn' and fishermans % 2 == 0:
    trip_price -= trip_price * 0.05

if group_budget >= trip_price:
    print(f'Yes! You have {group_budget - trip_price:.2f} leva left.')
else:
    print(f'Not enough money! You need {trip_price - group_budget:.2f} leva.')

Аз го реших така:

budget = int(input())
season = str(input())
number_of_fisherman = int(input())

ship_rent = 0

if season == "Spring":
    ship_rent = 3000
    if 0< number_of_fisherman <= 6:
        ship_rent = ship_rent - (ship_rent * 0.1)
    elif 7 < number_of_fisherman <= 11:
        ship_rent = ship_rent - (ship_rent * 0.15)
    elif number_of_fisherman >12:
        ship_rent = ship_rent - (ship_rent * 0.25)

elif season == "Summer" or season == "Autumn":
    ship_rent = 4200
    if 0< number_of_fisherman <= 6:
        ship_rent = ship_rent - (ship_rent * 0.1)
    elif 7 < number_of_fisherman <= 11:
        ship_rent = ship_rent - (ship_rent * 0.15)
    elif number_of_fisherman >12:
        ship_rent = ship_rent - (ship_rent * 0.25)

elif season == "Winter":
    ship_rent = 2600
    if 0< number_of_fisherman <= 6:
        ship_rent = ship_rent - (ship_rent * 0.1)
    elif 7 < number_of_fisherman <= 11:
        ship_rent = ship_rent - (ship_rent * 0.15)
    elif number_of_fisherman >12:
        ship_rent = ship_rent - (ship_rent * 0.25)

if number_of_fisherman %2 == 0 and season != "Autumn":
    ship_rent = ship_rent - (ship_rent * 0.05)

if budget - ship_rent >= 0:
    print(f'Yes! You have {budget - ship_rent  :.2f} leva left.')
else: print(f'Not enough money! You need {abs(ship_rent - budget):.2f} leva.')

Имайте предвид, че на тая задача условието е малко подвеждащо. Говори се за "рибари"..."Тони и приятели"... съответно аз се подведох, че рибарите трябва да са поне двама. Това не е така. Бройката рибари трябва да е повече от 0. Т.е. минимум един-иначе куп проерки не излизат.