That is one way to look at it......
However I look at it differently....
Even if we stick with the 2/10ths of a percent (which from what I have personally seen is extremely low--I've seen it average from 5/10ths to 1 full percentage point), and we stick with the 65% cc usage (again low based on the shops I've encountered), Then lets suppose half of FTD's 20,000 members process cc through them. That means FTD would make an extra 3.25 MILLION DOLLARS a year by charging the extra 2/10ths percent because the "small business" florists "don't worry" about that $0.89 per day. If the rate difference were 5/10, they would profit an extra 8.125 million. Bottom line, is that FTD is intentionally making it difficult for florists to compare rates and shop around because they are reaping big profit from it. Period.
If we wanted to then examine it from a business (ROI) perspective, it IS most likely worth the time and effort of chasing down that $0.89 per day as well. Suppose the average florist pays themselves or their manager $25/hr. If they save $325/year as you suggest, then as long as it takes them less than 13 hours to compare rates, it is worth their time. (and this is only year one, the lifetime value would be much higher). I just shopped rates myself, and can assure you it didn't take me 13 hours. If you save 5/10ths of a percent, you now have 32.5 hours to shop for a better rate.
One of the biggest differences between a successful business owner and a stuggling business owner (in my opinion), is that a successful business owner pays attention to the small things. They don't let the $0.89 -per day slip through the cracks. Everyone notices and pays attention to the big expenditures, but its the small ones that often have the biggest impact on the bottom line.