Well being someone who has bought & sold content, I'd say you get what you pay for. If you're looking to run the business for long, you want quality, which is something that $1/100 words can't offer (still possible but prob only 5% chance). NEVER use Fiverr to buy links. Do it right because it costs more to undo the damages.
I wouldn't trust fiverr with seo tasks. Try searching the forums - you will pay $5 more, but you will definitely get better results.
If your client is based in the U.S., it is worthwhile to get listed on the Blue Book directory (thebluebook.com). They are THE construction directory and just about every construction project is listed and advertised on it. It is very active and prime contractors use it all of the time to find subs for their projects. This should not be confused with Kelley's Blue Book which is focused on the automotive industry.