Master / alpha reseller web hosting
are these reliable
It's too difficult to keep track of how many users you've got on a server, and how many resources they've each been promised. Once you get to alpha, the end users are removed from the server administrator by too many degrees.
A VPS is almost certainly your best route, as you then know how much disk space / CPU and RAM you've got, and it's up to you to manage it.
I've never been too keen with Alpha reseller accounts because to be frank there's too many involded but the master reseller concept is something I find usefull to those starting out who want to offer shared + reseller hosting without needing the headache of server administration and the worry of keeping everything secure.
To get 100 GB reliably delivered as regular shared hosting, I'd say someone should aim for $40-$60 monthly (minimum). Reseller plans tend to cost (over-simplification) roughly double what shared plans cost.
I'd still recommend a VPS - but get a fully managed one if you don't want the overheads of managing it yourself.