Setting a DA cut-off from the outset is a bit too arbitrary. What if it's a link from a site with low DA and a low PA now, but later the site becomes the next New York Times? You don't want to disavow the next New York Times, but that's what an arbitrary number would have you do.
Further, DA and PA can be gamed to a certain extent. I'm sure Rap Genius has a pretty solid DA, but they were penalized all the same. So it would appear that using DA as a cut-off would be less than ideal.
There's no real easy way to do a disavow. You have to think about characteristics, context and intent. If you have links that pass juice, but were obviously paid - that may be a candidate. If there's a vast preponderance of links from seemingly low quality directories with exact match anchor text - those would be candidates for closer scrutiny as well. Dead giveaways are usually 'sponsored' links that pass juice.
Low quality directories usually let everyone in. You will know them by their viagra and casino anchor text. They're usually a pretty safe disavow candidate.
Does the site have a lot of links from spam blog comments from sites that are obviously unrelated? Has there been some guest blogging on free for all blogs? Those links would require some review as well.
Definitely prioritize your exact match anchor text links for review.
I would suggest you start with gathering link data from numerous sources:
- Google Webmaster Tools
- Bing Webmaster Tools
- Ahrefs
- Majestic SEO
- Etc.
Then filter the duplicates via spreadsheet voodoo. After that, drop it into a service like Link Detox. But be careful, it still throws false positives and false negatives. So again, there's no real way of getting out of a manual review. But Link Detox will speed up the process.
Are there plenty of disavow services out there? Sure, but I've never used them. I'm far too paranoid. A disavow is a delicate and lengthy process.
Are there some great disavow pros/individuals out there? Definitely. I would be far more likely to trust them. In fact, a couple will likely chime in here. Though they may be a little bit outside the budget. I don't know.
One final, important, point: A disavow is not a panacea. They take as long as they take. Though it is good that you appear to be proactive. You never know when the next Penguin filter will land. The site may be right with The Googles now, but it might not be later.