These types of costs are hard to quantify, because they are based on several factors.
For instance, you can buy a 400GB hard drive for $250, a one-time cost of about $0.63 per GB. Based on raw cost alone, you could theoretically give a user 1GB of disk space for $0.10/month and have the hard drive payed for after 6 months. However, in most cases you are going to run out of disk space way before you run out of other resources, and so you won't be able to use most of the available space.
The same thing goes for bandwidth. As your users use more bandwidth, they're also consuming CPU and memory resources to do so. $1/GB is the usual rule for data transfer.
No offense but that's like asking how much a car costs.
Now if you provide a manufacturer, model, list of features. location where you'll buy from, sales tax, and all the rest of the relevant information you could probably get a pretty accurate price for that car...
Definitely highly dependent on several different factors. I would suggest doing a little research on dedicated servers and colocation, and you should be able to find an appropriate cost/unit, considering a few factors you predeteremine, such as general overhead aside for servers, expected profit margin, etc.
I'd say anywhere between $35 and $100 per mbps. Just for fun, lets use $75 as this is a quote i received for some -good- bandwidth.
128 Kb * 60 secs * 60 mins * 24 hours * 30 days = 331776000 Kb per month
324000 MB per month
316 GB per month
$75 / 316GB = $0.24 per GB per month
So, with a 1mbps commit, without bulk pricing, or cheap bandwidth, it looks like about 24 cents per gigabyte. But keeping it sustained isn't likely, and it'd be hard to actually get that much out of a 1mbps commit. But its possible.