How Do I Make A 1 Time Product Charge (Logo/artwork Set Up Charge)?

Hello-

Are there any vendor/developers that offer an add-on to make a 1 time product fee?

Example-

1. Customer is ordering 10 custom T-Shirts with all the same artwork.

2. We need to charge a 1 time artwork/logo setup charge on the product page of $20

3. Currently if the customer adds an option that has a price, they are charged that

option amount multiplied by the total quantity ordered (in this example 10 x $20 = $200)

4. We need the customer to only be charged the $20

5. We would also need the for the customer to not select the logo set up charge if

a. They order over a certain quantity of T-Shirts (50+ = Free Set Up Charge)

b. Have no custom logo and are using a stock design

Any input would be helpful.

Thanks,

Kevin