I think the danger with this is that, like lots of things in life, some people will go too far and build services with cheap price without really considering the real costs for having a customer and the support and maintenance will be difficult.
It's easy to have 50 users at $6/month, but having 3000 users at $6 will only returns 18k. How much resources (human and technical) is needed to handle the load of 3k paid customers?
For me I prefer having open source projects, like the one I'm slowly building on the side here Parle.io which is an Intercom / Drift open source version.
Revenue model? I will have a commercial license, and just like Ghost I might offer hosting, but I would prefer not. Offering a self-hosted commercial license + the FOSS one kind of sound easier than operating a "cheaper" SaaS where support and quality of services (as in your infrastructure) needs to be up for 99% of time.
Like everything, it depends :). I would not want to see lots of new SaaS emerging with only price as competitive advange. Where's the creativity in that? What's the fun part of building XYZ and just making it cheaper?
Also what happen if, for example of @SteveMcLeod UserVoice were to open a free plan [just picking that example because you mentioned it]. We do have a free plan at Roadmap to grab user feedback. But I've not designed this based on UserVoice for lots of reasons which are out of scope here :).
Having not done a ripe off if UserVoice were to open a free plan it would not affect us at all, since we did innovate re: capturing user feedback.
I'm not implying that FeatureUpvote did not innovate (I did not looked at your product at all Steve). Just to be clear here.
That's an interesting subject I think.