When I was running millions of rows of data for a government client, having Oracle support basically on call 24/7 was nice and it was used multiple times in the 4 years that I managed that system. That is why the company paid for Oracle, plus the security, performance, documentation, etc. The other big thing is that we had SLAs with our clients (mainly government and fortune 100 companies) if we didn't meet those SLAs for any reason, we were in deep shit for the money we had to pay out to those clients in form of credits or even legal fees for law suits. It is cheaper to pay for a package like Oracle that can give you the SLAs and help you in the event of an outage so that you are less exposed to risk. Most large corporations will make decisions not on cost, but on risk mitigation. How much will it cost IF it fails? More on reddit.com

Any particular reason it has to be Postgres? If the application barely needs to be opened i'd presume SQLite would be more suited for the job More on reddit.com

Prefacing this with I work for AWS, but not involved in billing, marketing, or sales. I’m also a customer for my startup. The cost per hour is simply for up-time. If your database is always live then multiply that amount by 750 (number of hours in a month, more or less) and that’s approximately your monthly charge. There are also some data transfer fees associated with it, but unless you have a HUGE (and I mean HUGE) amount of traffic, these costs will be insignificant or possibly $0 since there’s a free tier limit. If you turn your database off from time to time then you do not get charged for when it’s off. You can set up lambdas to automatically do this for you. The costs per hour vary by region, type of language (MySQL, Postgres, Oracle, etc.), and size. Really size is the biggest factor - how much storage you need, how fast you need it to run, etc. There are additional costs associated with having a read-replica (or DR- Disaster Recovery) backup of the database. There are free tiers you can use that cost nothing (or close to, depending on data transfer costs and storage) for the first 12 months, but these are very low-power servers that will take longer to return results for example. You can also apply for AWS credits through their Proof of Concept program or AWS Activate Founders program. Our bill is $450 or so per month for a few different services (probably around $250 for our PG databases), but we haven’t paid anything out of pocket in over a year due to the credits we’ve received. You can also set up budget alerts so you get emails when your actual costs reach a certain threshold or when forecasted costs reach a certain amount. Also for when your actual costs reach a percentage of monthly budget. Be very careful with AWS billing - it’s easy to lose track and end up with a bill much greater than you expected. Set up budgets and alerts early so you can get ahead of it. I recommend starting w a free tier and if you need a more powerful server you can upgrade at any time. Cheers! More on reddit.com

You want an awful lot for exactly no money. More on reddit.com