You won't find those specs in the price range you're looking for with a reputable host that you can run your business from.
Just look at some of the premium VPS providers, knownhost.com, linode.com, hostdime.com. In the $50/mo range you'd get 1GB RAM, 60GB HDD, 500GB-1TB BW. Those hosts are going to give you rock solid service, with little interruption. That's who you want to base your hosting business foundation on.
You can go with many other unmanaged budget hosts that are cheaper, but you run the risk that your hosting business goes down more often with budget hosts that may not be as reliable.
Your budget seems appropriate for servers without cPanel. Servers with cPanel and managed support with this kind of configuration is a rare combination to be found. Also let know if your quest ends, and you find a provider to fit your needs, as others can benefit from it too.