You listed the frame for a price you thought was reasonable and would be happy with if sold. People are willing to pay this price. Now you think people might be willing to pay more, you're unhappy. Why?
I'm not from the UK and therefore not familiar with the situation surrounding the NHS. I'm just trying to understand where you're coming from when it comes to your concerns.
Raising the price now is a definite no-no.
You listed the frame for a price you thought was reasonable and would be happy with if sold. People are willing to pay this price. Now you think people might be willing to pay more, you're unhappy. Why?
Admittedly £25 for a sound frame is not a lot.