A lot of the SAAS offering usually say something like "for just the price of a coffee a day you can get our service" but If I was to pay for every services I use daily I would need a third job.
The reality is that paid services are not immune to be shut down, for example after an acqui-hire. See Astrid, Sparrow and many others.
Heck, even services backed by a web giant like Google are not immune either, they can always decide to shut it down like they did with many of their services.