Hello,
The minimum price should be the price you're comfortable/happy/need to sell at.
For Example, if you really want to sell your domain for at least $300 but you need $100 to pay your bills so that is the lowest you'll accept, then your minimum price might be $100 because you can at least pay your bills at that price even if the domain is worth $800. Sometimes you might risk a lower minimum price to get more activity/bidders interested (Which can result in a higher sale price than if you had a higher min price), but you have to be willing to accept that risk and understand that it might pay off or it might not pay off.
Hope that helps,