Cost depends on your host company.
If you are reselling, the object is to divide the cost between your customers / users and add a bit on for your bother.
My web hosting costs £30 a year all in including the domain name.
Maybe your option would be to find a hosting company that is cheap and gives you unlimited traffic, bandwidth and enough serverside resources that you can then operate as many single user accounts and you act as a broker.
A word of warning though, domain registration... The web hosting comapny I use has an account with a domain registration company in the USA.
Whilst the domains registered are .uk TLD's, the main issue is that the actual company that does the registration sends out letters warning people that their domain is about to expire.
What is wrong with that is they are cutting out the broker who I use and trying to dupe me and others in to parting with sums of money that they will have no right to and also be creating a deadlock situation where I for example if I had paid the company be in ownership of a domain I could neither use or transfer out of the hosting company...
Thats one dirty little trick you would have to watch for and be aware of because the domain registration company will have had its money and run.
So, do you still want to resell?