Quitting over decline in quality

If you're fastidious about code quality then working in a startup that doesn't have a huge runway of cash in the bank is the wrong place for you. Sometimes you have to compromise what you're making in order to keep your head above water - "Done is better than perfect" to use the appropriate startup adage. If the money isn't there then the quality of the code won't matter. You can always go back and improve quality when things are better.

As a developer rather than a founder you need to ask for as much transparency as possible. Your job is to spend the appropriate amount of time on a feature to make something that works and is "sufficiently high quality"; the founders job is to give you enough information necessary to make that decision (or to make that decision for you if they're technically capable).