We just released the beta version of our web product to our sign ups. Our product design is moderate since at this stage, we are mostly looking into validating our product, but we understand that it needs major UX/UI work soon. Like most start-ups, our team consists of one developer and a CEO with limited financial resources; which leads us the question: when do you think an early stage start-up with a web/mobile product should seriously consider bringing a full-time designer on board (equity/cash) and how should they get design work done before that stage?
Speaking as a UI/UX designer, I think at your stage you should do as much of it as you can. In reality, it's your only choice if your finances are limited.
The CEO and/or the developer should be learning as much as they can to try and make the product as attractive and easy-to-use as possible.
Look at other apps for inspiration. Use CSS frameworks like Bootstrap. Read books and blogs, take online courses to learn the fundamentals of user-experience research (how to prototype, common design patterns, how to perform user-testing) and web design (typography, color theory, usability basics).
Will you be as good as an established professional with years of experience? No, but you don't need to be right now. Focus more at this stage on whether or not your product solves a pain for your market. Make it as great as you can make it on your own. The first versions of Facebook and Google looked like shit and it didn't matter.
Once you have proven your market, perhaps you've raised some money or have revenue from your product, then go out and hire a designer to make it look beautiful. Most of the fundamentals of UX research can be learned by anyone. As an entrepreneur, when you are low on cash you need to be that much more scrappy and DIY to get the job done.