How much to charge as an IT subcontractor

Hello,

I have been approched by an IT Consulting company to do some moonlighting work. (installing and maintaining servers / switches firewalls etc) Pretty standard stuff. His business would be the primary contractor and I would just handle the technical work.

Thus individual would like to know how much I would charge on an adhoc hourly basis.

I would like to ask a percentage of what he normally charges for an hourly rate.

My question, what would be a respectable percentage of the hourly to ask as an I9 situation subcontractor?

Would 50% of his hourly rate be a good number to start at in negotiating this?

Thanks!