There is always a market for cheap high DA links
If this is dressed up as a directory, then so be it.
There are a few out there offering good niche links on business directories for say £3.99 with a follow link and they are very popular.
I think if you are happy with taking this type of money via PayPal, offering a hands off directory on decent domains (DA) and then remarketing to those who paid for a link - as they will be the SEO types with a budget for shit links it might pay pretty well i'd say!
I've also seen very high priced directories, guess this is up to you which way you go.
Personally (and i did look into it) - i'd be setting up loads taking small donations and trying to get 4/5 payments per customer per site. You'd be laughing then