Privacy versus money
"The cost of securing a server is less than it once was. If you can implement https cheaply, it's well worth doing. But that won't be £500 for all sites. Your website might use a content management system that wasn't designed with secure forms in mind. Making that change can cost a lot more than a few hundred pounds."
I am not a lawyer, but I somehow doubt you would be successful if your defence consisted of "we bought a sub-standard CMS system that wasn't capable of securing the personal data it held to an appropriate standard unless we paid someone shedloads more wonga - which we didn't bother to do" ....