Our shop is 2 technical founders and a business guy. We don't have a bit of design talent between us but we have bootstrap! Our software is a utility for viewing and codifying large sets of data.
As soon as you can reasonably afford it ( if you can't pay, go get another cofounder ). The web has evolved from simply working to working seamlessly. Consumers expect a certain level of aesthetic and usability.
Design is one more element of your product, just like solving a real problem and doing what it's supposed to do.
I would prioritize a designer as much as an engineer. I have seen a huge difference I product adoption when the product is complemented with visually pleasing aesthetic and good usability principles.
