It depends. Firstly, what stage of a startup are we talking about? Are we talking a guy building just a landing page? Are we talking a 20-person team with VC?

It depends. Firstly, what stage of a startup are we talking about? Are we talking a guy building just a landing page? Are we talking a 20-person team with VC? The answer is different for each case, both because of the money available, but also because of how much that design will end up being used. A landing page that might never lead to a product shouldn't cost you $1,000. I haven't had much experience on the later stages of a startup, but I have built a few products to the beginning stages. Early on, I made the mistake of building the product without a design first thing. I figured, if it gets good feedback, I can alway redesign it. Instead, what I would do today if I were building any product is go buy a template for $50, and work off that. Saves a lot of redesign time (which is harder to do, since you've already got legacy code). Also, gets you the "good design first impression" right off the bat, which will lead to more accurate results when you need them the most (since you really don't know if the product will be a success or not). For a landing page, which you should do before building a product (unless the product is really simple), I've recently learned the best way. Go to WooThemes.com or ThemeForest.com, buy a WordPress template for $70, and it will make setting up your landing page a Wysiwyg experience, which is much better. Even if you're a programmer like me, trust me on this, using WordPress will make things smoother, and the design will be better for it. As for an actual startup with an actual product (and money in the bank), I wouldn't even think twice: hire a designer.