Here's a set of different design options, broken down by budget, from the Folyo blog.
- $0: Use a free framework and UI freebies
- $0-$100: Get a pre-made theme and nice typeface
- $100-$500: Consider crowdsourcing
- $500-$1000: Crowdsourcing or freelancers?
- $1000-$10000: Get a good designer
- $10000+: Agencies
The anonymous author also describes each of these options in some detail and proposes some options. Definitely worth a bookmark!