A backend most definitely is worth 35 mere dollars. Though (you guessed it) it depends. It depends what you are going to do with it since maybe you can get a static site with a JSON shipped to the client and usually achieve similar results.
But, consider that by buying the cloud service you get: - database - probably a server with their hosted thingy (maybe a node.js server) - maybe some monitoring microservices as well
The question is then, - Does the time of setting the stuff up yourself, and the probable issues that come with it -- are they worth the marginal 15 dollars? This questions gets you the answer.
(Not to mention that some images of supposedly OSS microservices usually are different that their cloud service.)