The reason I am buying the "cheapest" seeds, is because I am trying a new seed bank and don't want to lose $100. Plus the fact that they are produced by sensi seeds makes me think they are decent seeds. A lot of the White Label seeds are priced right up there with the Sensi strains, so I wouldn't call them cheap.
I have been growing for a little over 3yrs now, and I have figured out that genetics play a huge role, trust me. I even went as far as to attain a horticulture degree, so I have a basic idea on how this seed thing works. And if I get some "cheap" seeds, and end up with one great pheno, thats all I need to make it worth it.