Most lawyers have these already, and although they'll certainly charge you for the domain knowledge, you shouldn't have to pay hourly. You should be able to get a good, generic NDA for <= $500. NDAs are really simple, and usually pretty short.
I've never tried docstoc et. all, because part of the value for me is having a domain expert say "yes, this will cover your specific business needs."
One other thing: I've seen a number of companies providing their NDA on the contact / quote request page. I've been considering the same, as it might be a good way to head these uncomfortable conversations off at the pass.
Edit: this is a great place to barter as well. What you want from the lawyer is their expertise, not their time, and lawyers know the ROI a good website can bring them. I'm sure you know some lawyers, ask one of them if they'd be willing to barter a website in return for a set of documents. If you happen to be an SEO (I know, dirty word around here), offer that instead - one of my clients is an attorney, and the #2 Google ranking we helped him achieve yields thousands of dollars each month.
Feel free to use mine (http://markwatson.com/consulting/nda.htm) but if you improve it, please share your changes back with me.
After just re-reading my own doc, it is probably too long. It used to be about half this length.
HOWEVER, I frequently delete or amend small portions of the NDA before signing and explain to the client why I have done so. I've never had a problem so far.
Once I had the president of a company (new client) tell me how much he appreciated me haggling a bit. This guy was a lawyer and told me he was surprised by how often people just sign stuff. Anyway, his telling me this after the fact made me feel much better about haggling in the future.