That's a red flag!
The way you describe your potential link sources triggered so many red flags in my mind.
Your best approach is probably to avoid looking for cheap link sources and focus more on targeting niche-specific sites that you can hit for guest posts.
If these sites rarely get any requests or are up and coming, you may be able to get lots of guest post links for them for very little to even no money.
You have to remember that a lot of specialty blogs are hard to maintain because of content creation costs.
If you come along and you convince them that you can produce content that matches their current quality level, they will give you the keys to their site.
Don't be all that shocked if you get a lot of takers.