TablePlus (https://tableplus.com/) is my current goto - even has a nice iOS app for on the run queries. I have fond memories of Sequel Pro and this app scratches that itch.
I think trying to justify their pricing on hosting alone misses their point. Nothing fundamentally changes in hosting, probably in any environment. However, the development workflow does change with extra team members. Netlify's tools for collaborating are fantastic. I think that's the value they're pricing.
Experimentation is another good option, and goes a long way, but it can be scary. If you're at all worried about doing permanent damage, install a virtual machine (i.e. VirtualBox + the server version of Ubuntu or whatever OS you want). That way you can experiment away without fear of doing permanent damage. If it happens just trash the the VM and start again.
Ultimately a prototype is just a tool for learning and discovery. So what you build depends on what you're trying to learn or work out. I've built prototypes as powerpoint decks, basic HTML/CSS, and as apps built in Rails or PHP. Sometimes with a database backend - or with some spoof of one.
If your goal is to create cool stuff now, you don't necessarily need to learn how to program. You can build prototypes in PowerPoint or Keynote. My partner and I built http://www.thankthanknotes.com in 8 hours using Wordpress, a pre-built template, wufoo, paypal, and almost no code.
Now, if you have a genuine interest in programming that's a different story. I do know it's taken me years to become a half-decent developer (I come from a design background). So, have some patience. What do you do now? Did it take 9 months to be come proficient? But don't let a lack of dev experience/knowledge keep you from building something cool.