How to critique promotional videos?
A quick google and the 3rd result is this article on how to write a product review...

Finding examples is easy, just do a youtube search or google "Canon 550d Video Review" or any other product event or service. Just add "video review" to the end.

I dont think you will find any specific tutorials or resources on how to produce review videos. Making good review videos comes from experience. Either because the producer has been educated in writing &amp; marketing or because they have done it many times before and have worked out what 'works' and what doesnt. Just look at the reviews that are already out there  and model yourself off those. 

Cost is simple: What equipment do you need?


Camera
Lights
Microphone 
Editing Software (eg Final Cut)
Editing Hardware (eg Laptop)