Once you decide which pump and lights to use, it's a math problem from there. Your power cost is by kilowatt hours. With LED lighting, it shouldn't be expensive. I'd say the initial outlay will likely be your biggest concern.
Humidity shouldn't be a problem if it's not already.
to address the increase in humidity you can use a dehumidifier and use the water that you collect from it, it can go back into the system.
If it helps any, my LED grow lights cost me about $.40 per light per day to run, while 400w metal halides were costing me $1.00 per light per day. I have two lights that are covering 21sq ft of grow space each.
I also recommend a dehumidifier if you want to avoid water damage. It will also keep you from having to top off your system water as often. They can be heavy load on your electricity, so shop around and find one that's relatively energy efficient.