Well, I add 5 extra grams pressure and can use it for another 3 months, I pay about $25 for a knife, I wouldn't call it very cheap.
How much money are you making with that $25 blade? I just did 6 rolls of 30" reflective without needing to change the blade.... About $7000 in Proffitt.... And likely won't need to change it for weeks. For me ... That's cheap, especially when you compare it to the income it brings in.
Also... If you have to keep adding pressure to all your cut conditions (we use 5-6 regularly for different vinyls) or spend an extra few minutes weeding here and there because you don't have a perfectly sharp blade, it likely adds up to more than $25 in labor!
If your blade is set right and you're only cutting the vinyl and not the paper, the blade should last a long time. Squeezing an extra few weeks or months isn't worth it for the headaches it costs.