What they all said...
See, the thing is, 'I don't have the man power' is actually not a legally valid reason to withdraw from a contract in the state of California, where I gather from your profile this happened. So if this job was indeed properly contracted, not only do I not pay you the markup, maybe I sue you for breach of contract instead, since it will no doubt cost me more now to get the job done. And in fact if I just take your materials and don't pay you
anything, your only recourse is to file a lien for the cost of the materials. But in order to actually perfect the lien and get paid on it, you'd have to take me to court, (which you can't afford to do, so maybe arbitration instead). And the judge, er, arbitrator will likely agree that since you are in breach of contract you owe
me something that should be subtracted from whatever I would have owed you for the materials, which depending on how much I can show I lost may be more than the materials themselves.
So... if I offered to pay you the cost of materials
minus your markup, you'd better consider that I'm being very generous because I understand how difficult the labor market is to deal with right now, and you should take me up on that offer and hope that I don't badmouth your name to anyone I know who works in the same business and for whom you might want to work in the future.