As an entrepreneur, here are my 2c, start with charging what you believe is an obscene amount (though within the bounds of the reality of your field, just make sure you're in the more/most expensive side of things).
Make sure you keep in touch with everyone you've sent a proposal, and if you don't hear back in a certain time ask why, if they name the price as an objection you can always offer them a special discount, (only for them
) because you would really like to work with them, or whatever reason.
People won't ever say, you're price the first time was waaaaaaay too high so now I'm not going to talk to you anymore.