If you're working on a startup that is not yet profitable (or at least compensating you for your time), your time is currently worth close to nothing. That same time may or may not have a higher value later.
That's only true if you have no money and have the means to live completely for free. Otherwise, if like most human beings you have some expenses, than regardless of whether your time is producing value it certainly has a cost, and that can be directly compared against the cost of a PaaS.
That depends though on the current value of the start up, which could very well be close to zero.
Say you could be paid $100 p/h at some other company, but instead your start up is paying you $5 p/h because that is all it can currently afford.
Say you can save yourself a weeks work by going with one hosting option that is twice as expensive but the total additional cost would allow you to work for $5 p/h for an additional two weeks then that isn't a great trade because the "value" of that labor is both unknown and irrelevant at this point. It might be $0 p/h or it might be $10000+ p/h.
1:1X dyno on Heroku is free, with a postgres server, and a free redis instance.
So even at $5/hr I can't justify doing this work myself at this point, since I can get the infrastructure for my minimum viable product going for free. I can and should spend my time focusing on developing the features.