Hello there!
If you want to support the devs but have a limited fund for doing so, you can limit the monthly charges by a certain number (minimum 2 I think). So if you choose Pony Tier, you can have a minimum monthly charge by 6 Euro (in my currency it is 3 Euro per Post). Setting a limit won't restrict your access to anything (at least in my experience). This how you can control how much you pay.