There is another way to think about this. Instead of working for one startups, work for several.
I have probably done work for around 100 different startups since I started my company in 2005.
What really helped me though was that I started the company with Morten Lund (Early investor in Skype) who had several companies in his portfolio and a good connection in the venture capital world. That helped send work our way.
Instead of going for design conferences go to conferences with a lot of VC guys. Show your portfolio around and you will most likely get some work if it's good.
You will need to be a little more flexible with regards to pricing but that can be solved once you realize how most startups get their funding.
In the angel round, companies are normally pretty cost sensitive.
One way to solve that is to charge less than your normal would but with with an option to cash in if they get their series A funding.
This is a great motivator and that is only one of the many many advantages of working for startups.
