So we launched
https://emailoctopus.com around 3 years ago, it was pitched as 10x cheaper than Mailchimp and that's remained our core proposition.
That said, it's very difficult to grow a bootstrapped business when you're not charging much. At the lower end of the market you usually have less committed customers and depending on the SaaS, you may attract less favourable customers. As such we're slowly moving away from pricing being our only unique selling point and beginning to look at differentiating features.
Copying features at a lower price is a fine way to start out as a one-man band and gives you sufficient focus to get it out ther door, however, to grow the business I think you'll need to look bigger.