I would have to say that your "cost" should be much less. I guess it depends on where you live.
Icing and ganache $50
No more than $30.00
Fondant $75 (4.5 kgs)
Homemade marshmallow fondant would be about $25.00. Not sure about cost for premade.
Cake mix $50
Should take no more than 8 boxes of mix. It's $1.14/box where I live so $9.12
Ingredients (eggs butter) $20
Depends on type of board used.
My quilt stencils were around $5.00 ea. so that's about right if you need them shipped to you.
$5.00 at most
No more than $4.00-5.00. I use those big straws with dowels in the middle. Straws are $1.00 for 50 and 3 ft. dowels are less than $1.00 each at the hardware store.
Inside boards $10.00
Are you using regular cardboard cake boards?
If so, no more than $5.00
What kind of box are you using? Typically, you only need the box to get the cake to the event.
I use regular moving boxes that are about $3.00 each. I do leave a small box for the anniversary cake. I buy them in bulk for less than $1.00 each.
Tin Hire $30
Not sure what this is?
Fake foam layer $20
That's about right if you order them online and have to pay for shipping.