All good points from Austin, Ali, Daniel and Lee, and I agree: branding is one of the most important elements of your business, even (especially) as a startup. Investing in it is simply a requirement, like getting a bank account.
But, that investment doesn't necessarily have to take a form of cold cash. Bringing on board a design-minded co-founder is an excellent idea brought up already, as with using crowd-sourced design services like 99designs.
Here's another way to think about it: your brand is more than your logo, or even the look and feel of your product. It's not a product or result; it's a process. Invest *your time* on thinking about what makes your product unique, who will be using it and why, and why it excites you guys (among other such questions). The results of your thinking about these questions deeply and having dialogues among you and with your constituencies become the basis of your brand. In fact, without this part of branding "process," whatever look you will come up will surely not be as effective as it can be.
The Brand Gap and Zag, by Marty Neumeier, are the two books I recommend every business owner read, regardless of their "design" expertise. There are lots of questions in them that you can ponder for a long time to come, and I am sure it will pay off in the long run.