lol, you can attempt to do it for $20 but odds are you won't be overly pleased in the end, nor will your clients.
Quick list of the top of my head to get started:
- Billing / Support / etc (WHMCS for most)
- Sitebuilder License
- SSL cert
- Video Tutorials
- HostLegal docs
- Domain Reseller Account
- Merchant Accounts
- Website / Logo
That list could go on and on depending on how much $ you're willing to spend from the start.
it is unclear what you are going to start. assuming that you wish to start a website, it can be even done for free (e.g. using google resources, yahoo geocities, blogger.com etc). of course you need to spend lot of time in preparing the site and advertising it.
I recently started up, and so only spent $350+ (including website design, software licenses, advertising etc).
As mentioned above, if you were really serious about starting up (i.e. you were happy to start off with a dedi, pay some part time sales staff etc), you could easily pay $x,xxx
Although, if you were happy to code and design the website yourself, and didn't want to pay out for advertising and software licenses, your only start up cost could be the reseller account itself... so, ~$15 per month.