Alright, the question is how oversold is the VPS node? What kind of network is backing it? Are you providing complete management? At $45/month with cPanel for free that $30 in revenue you're generating for 4 cores and 8GB of RAM. Considering your system probably has 12 physical cores, and another 12 hyperthreaded (typical VPS setup), if assigned 32GB of RAM you're looking at 5 VPS nodes if you're overselling the server. Cost of an average server with the above specifications is pushing $120-199. The only way, as a provider, that you'd be generating revenue is if you were overselling the server quite badly. So I'm guessing you're using OpenVZ for virtualization, because I know Xen wouldn't allow for overselling like that. Even the space too, 400GB * 8 = 3TB so I'm guessing a Raid-10 configuration? Brings up hardware costs right there as well.
It all comes down to this, if you're paying cheap for a hosting provider, you're going to get really cheap service, and if you plan on selling space on really cheap service that you purchased from a really cheap provider, your customers are going to see this as well when they notice that they aren't being provided with the quality that they do deserve.
Picking a decent provider that offers reseller cPanel hosting is not only going to lower your initial costs, but you are buying into a service that is taken care of. Start off by purchasing a basic shared hosting account with the provider, most of them will even give you a 30 day trial if you ask for it. Run some benchmarks, test things out, make sure that it's fast and can handle traffic accurately. Remember, these are all things that your customers are going to notice as well when you sell them services. If you are satisfied, as most providers provide a 30 day money back guarantee (minimum), ask them to apply that toward an upgrade to a reseller account. They will love the idea, not only are they going to be generating more revenue from you, but as you are getting involved with the industry you provide them with stability as a customer.
Start of small, there's no reason that you should be jumping in head first. The industry is very competetive so it is going to be very difficult for you to get your first few customers, but don't go the shifty route, don't offer under-priced hosting. If you offer hosting at a decent price, provide quality service to your customers, you are going to have more quality customers sign up for your services.
Elixant Technology started off as a budget hosting provider, initially offering $1.99 hosting, $49 dedicated servers and $15 VPS (1 Core/512MB Ram), and it was probably one of the stupidest decisions we ever made. Not only were we flooded with spammers, fraudsters and hackers, none of our customers stayed for more than a month as they were looking for that quick discount hosting until they could find something even cheaper. These are not the kinds of customers that you want to attract. We raised our prices, even now our Shared Hosting is pretty cheap at $4.99 a month, but at that price we've started to attract more reliable and professional customers.
In the end, it's not about finding or giving the cheapest deal out there, it's about the quality of service that you provide to your customers. Remember, 90% of the customers that sign up for your services in the future will be due to word of mouth advertising.