Number one, your sense of scale is wildly wrong. Number two, you're forgetting the rate at which you'll scale. Number three, you haven't done good bandwidth shopping.
First, if you have a hundred videos doing ten thousand views per month, you're serving a million videos per month. There is essentially no situation in which all of your users will watch all of your videos. A much more reasonable distribution is a gaussian curve peaking at 30-40% usage in pornography (not many other internet businesses use numbers like you do.) That suggests usage of about 350,000 videos, which cuts your costs in thirds.
Second, you don't need all your bandwidth up front. Just set up one cheapo VPS box to do routing, and watch your bandwidth use. When you get near 85% of capacity, purchase a new hosting program. It'll come online in a few hours. If your business model is viable, this should let you scale very smoothly. You don't need it from day one, and you don't know how fast you're going to scale.
Third, you shouldn't be looking at dedicated hosting. VPS is just fine for any non-security-related hosting.
Here are two companies that'll give you half a terabyte a month for under seven dollars.
Now, assuming the more reasonable rate of 350k videos served at ten meg per video, you're looking at about 3.6 terabytes. You can spread that across seven of those hosting accounts for about fifty bucks a month.
Looks a lot different now, doesn't it?
