I'm a bit disappointed that some people would dissuade an unemployed person from trying to make a living. A fair warning is a fair warning, but if someone's trying to work and asking for help, I think people should give him a little break and try to help.
Eltano1, you should charge as much as you reasonably can. You should have some idea of the customer's ability to pay already, and should bid accordingly. If you bid too low, you short-change yourself, if you bid too high, your customer won't go for it. If you have to err, err a little on the high side and you can negotiate down.
If you think that this customer is difficult - difficult means either that they won't pay, or that they'll hassle you down the line - then I would suggest walking away or bidding very high so they'll decide not to use you. Most of the time, you can tell pretty quickly what kind of customer you're dealing with. Some folks are really into rules and procedures, and some folks are just %$!%$#%s. Don't do business with someone you think isn't going to pay, or is likely to sue you, in your current position. You need to be a real corporation with real legal protections and ability to eat losses before you even mess with such customers. (my advice is still don't, but anyway).
But if you think the customer is reasonable, then this can be okay. You have to start somewhere. This sounds like a relatively safe and easy job - you're using wall-mount conduits and running through that, and it's all low-voltage. Your actual expenses will be cable (500'/$30), conduits (?? but not cheap), boxes (ditto), jacks ($6-$8 ea), a basic tester ($50), a punch-down tool if you don't have one ($60), and probably some other incidentals. Make sure to know what your direct costs are first. Then you have two choices: you can bid fixed-cost, or time-and-materials. In the first scenario, you quote a rate, let's say $125/drop, and then you make it happen. If your actual time is quick and materials are cheap, you profit. If there's a problem or the customer changes things during the job, you might not profit. Time and materials is lower risk for you but higher risk for the customer. You charge actual expenses to the customer, and you charge a rate for your labor (say $75/hr).
Most customers prefer fixed-cost. You as the vendor should build margin into any fixed cost bid to cover unexpected things. So that would probably be the best way to lead.
Now, be aware of the accounting and tax consequences of self employment. Expect to lose half of your net profit for this job in taxes. In your current position you might be tempted to use the cash in your pocket now, and then you'll be short come next April.