Before I share ideas on how to spot an excellent jQuery consultant or developer, a HUGE disclaimer:
There are 3 characteristics you need to be concerned about:
It's important that the consultant has already done what you are looking to build. The first time you build something, it almost invariably suffers from unforeseen design flaws. It's likely they will be much more efficient the second time (or third time) they build the same thing. They won't have to think about the right way, they will just code. And, why should you pay for thinking gosh darn it!
Ask what worked, what did not, and what they would do differently. If you are going to be building complex functionality, the consultant should have almost certainly contributed to jQuery or built some plugin you can look at. Check out that plugin. Is it documented, tested, and have clean code structure? If so, you might have a winner.
Whenever possible, avoid the solo developer unless her name is Rebecca Murphey. A consulting team brings multiple developer's experience and talents to bear on an application. Even if there is a single primary developer on a project, we always have everyone review the project.
Find out what types of applications the consultant likes to build and verify that it resembles your application. Are you just adding sliders to a form or wanting an animation to add flair to a dull page? Look for a jQuery developer with a lot of design experience. There are a lot of other skills you might be interested in:
- Browser support - does your app need to support IE3?
- Internationalization - do you need to support other languages?
- Usability - does the consultant specialize in making applications usable for the impaired?
- Comet - Comet can change how an app is built.
- Testing - How does the consultant test the application?
Unfortunately, quality jQuery developers are expensive. I don't know anyone great who charges under $100 / hr.
How long does an application take? This depends on a lot of factors. If the application has a lot of custom components or controls, it can take much longer than something where jQueryUI and theme-roller can do 90% of the work. We specialize in custom applications.
Most projects we do last 1-6 months. A rich forum application, with a bit more complexity than Zoho's Forum, took us about 8 man-weeks, including adding testing and documentation. I consider this very fast for a production release. But, this cost over $30k.
Finding a quality developer is difficult. There are a lot of sites where companies post for freelance work. I don't know of anyone who has found work from these sites or the results. If you are looking for someone cheap, I would reach out on the jQuery forum and IRC for any developers who might be interested in a side project.