Thanks for asking ggsm555. Well as far as how much your electric bill will go up because of your light depends on your service providers prices. Your electric bill is measured in true power "watts" and billed by kw/hr, at least where I'm from. Now seeing as you have a 600w hps, and I'll give you worst case scenario here, your bill will probably go up 10-20$ IF you run it 24/7. Now if you do 12/12 you're not looking at much of a difference, maybe 5-10$.
Now about your concern on plugging them in together. If you are plugging them into the same receptacle, assuming its the typical 15amp receptacle, you should be perfectly fine. Electrical fires usually happen due to faulty wiring, or undersized wires. Now your light will be pulling 5 amps. I=P/E, (amperage=power/voltage). So I=600/120=5amps. Now assuming you are using a normal oscillating fan, they normally don't pull more than 1 amp. So if your using a 15 amp circuit and using 6 of it just for your setup, you have 7 amps for whatever is left on that circuit. You'll be good, no worries. Now if you are paranoid about a fire, go buy a power strip with a surge protector built in or a gfci built in. Or if you want to be reeeeeal safe, go buy and install a arc fault breaker on that circuit in your panel. Those are specially made to prevent fires in house and will trip in .01 seconds when a fault is detected. And of course if your not comfortable with doing the work and don't mind spending the money, hire a qualified electrician to do the work. Won't take more than 30 min.
Hope I could help you out there, and I didn't confuse you to much lol. Let me know if you need more explanation. Also, go ahead and find what breaker your setup will be on and find what things in your house are on that circuit. If nothing big, like a window unit, stove, fridge, dryer is on that circuit then you should be good. If its just some lights and plugs that have nothing plugged in you are in the clear.
Thanks muddy. You holler at me whenever you need man. Me and TBM talked about this thread and he gave me the goahead for the post. I'm glad I can help the AFN community. I love this place!
