I'd say at least 75% on everyday Mr. and Mrs. Jones type jobs. I say at least that because I know others mark-up way more than that and they have every right to do that. I think it's very reasonable to pay $35 for a specific light bulb and charge the customer $100.00. This IMO is what covers the cost of knowing where to get the bulb in the first place and the time it takes to go get it and buy it. This is something a lot of guys do not consider. How do I know this? I used to work for them.
On the flip side, if materials are costing $100,000.00, I dont think it's reasonable to sell it back at $200,000.00. Thats just my opinion.