Where does Hipmunk gather their flight information and prices from?
How does Mint grab all your debit and credit card information from your bank?
Are you familiar with web scraping? Depending on the volume, and type of data you are trying to get, it might work for you. It should at least get you through proof of concept.
Why scraping is any worse than crawling is beyond me. But again, it depends on the application. I built a concert search engine which scraped data from multiple sites. It is my understanding that all the concert sites are getting a bunch of data from published apis and then topping up with scraped data.
When they started, they used Yodlee, who now has an app store where you can build on that same platform. They have already done the hard part of integrating with Banks. http://www.finappstore.com/
I ask because I recommended screen scraping and have used it successfully in the past. Though I do think it depends on the application.