I should ask for a percentage off if the cancel for some reason.
Without going into detail because it's not attempt to give legal advice ...
Yes, you are thinking along the right lines.
Liquidated damages / "Penalty" clauses can be ok, but the amount you have to pay should reflect a genuine pre-estimate of the supplier's commitments to subcontractors, other suppliers etc. They should not be allowed to make up for loss of profit.
A clause that seeks to operate
in terrorem is likely to be viewed as a penalty by the courts.