, sorry I've been busy prepping for something my friends and I call, "Nerdsgiving." It's Thanksgiving for just my group of friends.
I just checked CGC's website and the cheapest shipping method is UPS at $10 for the first slab and $2 for each additional slab.
Assuming a submission of 30 books, at $14.40 per book ($18 w/20% discount), a $5 invoice fee and $68 shipping, a total of $505 is $16.83 per book.
If you sell a slab for $25, the PayPal fee on that (separate of the fee on the addl amount paid for shipping) is $1.03 (2.9% + $0.30), which leaves a profit margin after slabbing of $7.14. That is over twice cover on most comics.
The same slab on eBay yields a fee to them of about $2.50, and reduces your profit to $4.64.
And since the turn around times are around 6 months right now, that means any slabbed modern that was released in the past few months had to be fast tracked. So that reduces the profit to -$6ish
Don't forget the cost of the book ($2.99-$3.99)+shipping supplies and now you're breaking even.