How do I add a fee per product after qty/disc price calculation?

My question:
How do I apply a $100 setup fee for customization after the price calculation of quantity discounting is applied? See sample charts below to visually understand my issue.

What I've tried:
I've tried attributes, which I may not fully understand, and right now the $100 is getting applied to every item, thus, an order of 100 becomes $10,300.00. FWIW, no, the custom fee as shown below doesn't have to appear in the cart.

Quantity Discount Pricing

Quantity         Price
----------------------
    1-49  at  $5.00 ea
   50-99  at  $4.00 ea
    100+  at  $3.00 ea

Shopping Cart

SKU   QTY   PRICE   CUSTOM FEE   LINE TOTAL
-------------------------------------------
CA     50    4.00       100.00       300.00
CD      1    5.00       100.00       105.00
CK    100    3.00       100.00       400.00
===========================================
ORDER TOTAL                          705.00

Am I missing something or is a mod what I need or what? Thank you for your time and help, including suggestions to improve my search* results!

*I am sure this has been covered somewhere but I am either looking for a needle in a haystack or using the wrong keywords (a combination of):
base, base price, price, price calculation, setup fee, quantity, discount, attribute, custom, customization, and/or selected verbs, etc.

Have you looked at the One Time Fee facility?

Thank you, I did, but it wasn't taking, so I've looked at it again.

A database error message popped up in the admin panel when I tried to access the attributes via the blue Attributes icon via Categories > Categories / Products (but oddly enough not when I had selected the the product via Catalog > Attributes Controller > categories dropdown > product), and it broke my site. So, I'm trying to get this resolved now.

Have no idea what broke but I am guessing that a core hack/mod to admin\categories.php for SEO purposes is at fault here. It'll take awhile to rebuild and get a default Zen Cart reinstalled for attribute feature testing/learning purposes, but this was needed anyway.

If it is a mod/hack-specific issue, I'll post the solution unless it was due to mine own hacking of a mod's core hack, i.e. I have installed the Ultimate SEO URLs v2.106 mod but have had to hack it to get it to do something a little extra while also getting it to function with other mods/core hacks.

May I suggest you leave the SEO URL stuff until you are done with everything else?