Would anyone here have an idea of how much it would cost to have a full roll of coins (Say Kennedy Half Dollars) still in mint packaging graded and slabbed?
Go to the grading websites? ANACS costs $14/coin plus return shipping and any other services you request, for US post-1950. You could submit at a show and save your cost of shipping. The others I don't know and am too lazy to look up for you.
I have never seen a roll deal before. There have been times in the past that I saved a few bucks piggybacking my coins with a big batch that my dealer was sending. I would go ICG. They are the most cost effective service out there. Easy to work with as well.
Dealer get bulk rates but that requires registering as a dealer (and providing whatever proof is needed) plus the quantity sent in is usually more than one roll.
PCGS and ANACS are not the same price and no TPG that I know of has a deal on a roll. It’s all goes by coin.
Several of the TPGs actually grade rolls AS rolls, but it's not a general customer level service. I've seen ANACS and NGC.
Being in original mint packaging makes absolutely no difference to them - any of them. So if you do decide to do this, do yourself a favor and open the roll, examine each coin carefully and closely, and estimate the grade of each. Then submit only the best of the best. You'll save yourself a lot of money. Also, be aware, only those with the highest grades, 69 or better, will be worth the cost of grading. And even many of those are not worth the cost of grading.
I'll also point out that a lot of people are confused about what "mint packaging" is, so post an image of an example roll so someone can verify. Not that it really matters - as @GDJMSP said you should evaluate each coin before wasting your money.
