You can hire writers on iwriter.com to write 500-word articles for $3 or 300-word articles for $2. The majority of them will be low quality articles because the premium and elite writers on there ignore low-paying articles. I used to write for them and that's exactly what I was doing.
Despite the low quality, they are still better than spun articles, so I suggest you consider this first. If you still can't afford them, search for an online spinner (they're free) and spin relevant articles from article directories.
That said, It's not advisable to use spun content on your PBN blogs. Spun content is a big footprint that can get your PBN deindexed.