I'm not sure I have an answer to your particular situation but perhaps I may be able to shed some light on why this happens.

I think there can be a conflict of interest when you try to link your income with (what you perceive as) your charitable work. I'm assuming you have this conflict of interest otherwise you would be quite happy to bill as highly as you can. It's the same sort of conflict that arises when people try to link their income with what they love to do.

On the one hand, most people have a feeling of vibrational lack regarding their finances and, on the other hand, they want to sincerely help others and/or do something joyful with their lives. So there is a kind of vibrational cross-current at work and both aspects suffer.

I have been in a similar situation to yourself where my income used to also be the source of my own form of charitable work. And I got myself into a real mess with it all. :)

I found my clarity eventually by separating the two aspects - and keeping them separate.

I have business interests now which generate a significant financial income (and I feel no guilt at all about charging highly for them) but I keep these completely separate from my spiritual interests which, if they generate any income at all, I simply reinvest into those same spiritual interests in some way.

This keeps my vibration about both topics clear and uncluttered - and, funnily enough, the two aspects are now not as separate as they might appear on the surface to an outsider...the Universe has a funny way of giving you what you want in unexpected ways when you feel confident enough to let go of struggling to do it yourself.

I know this doesn't help you in your situation right now but perhaps you now have some material to consider adding to a vibrational request. :)

By understanding that you provide a valuable and important service, a service that will cease to exist without adequate funding, and that you should be fairly compensated for providing that service. Know what you are worth.

If you have clients that can afford it, let them pay full price, because there are going to be instances where some cannot afford it, and getting full price from your clients who can afford it helps subsidize those who have difficulty paying.

Ethical quandaries like this happen all the time in the medical field. Most practitioners do the best they can with what they have.

One useful definition of inhibition is "inappropriate conscious or unconscious restraint or suppression of behavior, as sexual behavior, often due to guilt or fear produced by past punishment, or sometimes considered a dispositional trait." (Dictionary.com) I want to highlight the initial word "inappropriate". There's absolutely nothing wrong with charging the going rate for services provided. If you're charging too much, market forces will come into play and you'll lose business to others. But if you're providing a valuable service, then you deserve to be paid accordingly.

The issue seems to be related to your perceptions about what rates are reasonable and what payments are affordable to your clients, but on a deeper level, it seems that it may be tied up with a fear of what people may think of you if you charge "too much". You'll have to do some soul searching into why this may be the case. Sometimes there are religious teachings that cause some to feel that it is wrong to have more than a modest income.

To see money as a morally neutral tool that is useful for many good purposes can help overcome that particular type of guilt, if that happens to be the problem. Earning more money means you can employ others, you can make sure to keep the business running and growing, you can provide for your loved one and you can give to charitable causes.

It might also be helpful to understand that as a business owner you have a responsibility to make it a profitable business for the sake of your clients, employees and your own family. It would be wrong to let the business fail out of a misguided sense of being charitable.