https://selbstauskunft.net/ exists to allow you to send a BDSG §34 request (like GDPR request, but under the older German law for it) to basically any company. You select the company, sign it, and they automate all other steps.
I’ve sent dozens just this week.
Also, I'd recommend sending another request some time after quiting your contract with the company, just to make sure they give you a written guarantee that they deleted all data about you they don't _seriously have to_ maintain.
I also consider it activism to keep companies aware of their responsibilities.
Does anyone actually understand that this law will make things cost more?
Do you also argument against mandatory seatbelts? All they do is drive the cost of cars up. The justice system that works to enforce the laws brings the taxes up should we get rid of it too?
I certainly have several businesses in mind that I plan to send requests to once GDPR is in place.
EDIT: Although I suppose small, non-EU businesses that mostly do not deal with personal data are unlikely to receive any requests. So you are probably right that "most companies" are unlikely receive GDPR requests.