This may sound like a stupid question if you have an idea for a SaaS business. But a huge cost in launching a SaaS business is the actual web site - registration, sign up, free trial, monthly billing, secure access to digital products based on what plan is purchased. A CMS for marketing, integration with a chat bot and a service desk etc. etc. These are the mechanics of a SaaS business that are common. What you are actually selling is the product they pay for access to. Has anyone been able to buy such a service? i.e. an off the shelf SaaS web application - that you can plug in your offering?
We have used ChargeBee for managing the billing, plans, and free trials for one of our SaaS projects, and will likely use it for others as it works pretty well. We usually integrate Intercom as it's good for sending data from the product and using that to build tailored on-boarding campaigns. For the CMS we use Kentico Cloud or Webflow depending on the complexity and amount of integration needed with the website. For service desk it really depends on the SaaS product, sometimes it's just users interacting on Intercom or we would integrate Freshdesk - it's pretty easy.
When comparing proportionally with the amount of effort that goes in to build a SaaS product it's not actually that much. Marketing the website/SaaS is usually a bigger cost/effort.
We built a saas as hr software for human resource industry. Our personal experience in launching saas is that we segmented all cost and conversions. We are planning growth slowly so that our conversions balances our expenditure. Probably we won't expect any profit until we aren't a user loved brand and solution provider. Added the link above so that we can share some feedbacks. We are selling solution to automated the repetitive task. one of the biggest issue with sme or startups.
The integration between the product back-end and the UI is very specific, it would be difficult to provide an off-the-shelf package that didn't require a lot of custom code. I might start with a mature CMS that has good integrations for all the technologies I might want to use, and is also easily scalable, something like Drupal 8. That would reduce my development costs and allow me to focus specifically on integrating my product and building the UI.