Customer support/service is obviously vital to the success of every company. At a small startup where no one has free time or money, what can we do to improve our customer service without breaking the bank or spending hours on the phone with users?
All great comments above. In addition to everything already mentioned, consider the following: web-based searchable knowledge base with user forum so users can help each other without requiring time & expense on your end, video tutorials, and links on your website to quick reference guides that walk users through the most common issues they'll face.
Also consider outsourcing other back-office functions such as accounting and HR to free up your skilled engineering and product resources to continue developing a more robust product and documentation library to help you scale.