We raised $150k for our startup by crowdfunding. We did hire a PR company at the time, however if we were doing it again, we probably wouldn't. I wrote an in-depth blog post on it (http://allabout.siansplan.com/) but will summarise the relevant info here.
// Our experience with a PR company
Over the course of the campaign we were featured in (UK publications) the Metro, Telegraph, Sunday Times and many online platforms such as The Huffington Post and The Grocer. These were big wins for us, and 80% down to the PR company's contacts and expertise.
Publications however, were weary of posting anything about crowdfunding so the vast majority of these articles didn’t mention our campaign. The feedback from the publications with regards to our crowdfunding campaign was 'we'll feature your product once successful'. Other angles were used to entice the reporters to write about us (eg. reducing food waste, saving money, saving time). We then used our landing page to educate visitors about our crowdfunding campaign and how to invest.
We know that 4% of our investors (from a survey) found our crowdfunding campaign through the papers, a relatively small amount.
In short, a PR company will help refine your press releases, find interesting angles and approach publications on your behalf however it's unlikely that your crowdfunding campaign in itself will experience much traction in the press.