Electric motor for hang glider

I have been trying to do some calculations of how much battery power
would be needed to keep a hang glider flying level. With some help I
arrived at about 1 or 2 kW (a few horse power) for a typical hang
glider with 10:1 glide ratio and 180 pound (80 kg) pilot. As a
comparison, gasoline engines for hang gliders are 10 kW and give 1 - 2
m/s climb for half an hour on 4 litres of fuel.

I am unable to find electric versions of those powered harnesses being
sold. Looking around for battery prices I found this site:
http://www.hobby-lobby.com/flightpower.htm . The last battery on the
page is 22.2 V, 7.4 Ah = 164 kWh. I thought it may be interesting to
see how they would hold up when powering a human aircraft.

Each battery weighs 500 grams so with 10 batteries it would be a 5 kg
pack. The cost would be $500 * 10 batteries = $5000. Electric motor
with propeller and harness may weigh 10 or 15 kg on top of that, I am
unsure and would like to know figures. I have tried to find out but am
unsure of some of the terminology for electric engines. Also I do not
know if you can just attach a propeller to any old electric engine.

So it appears from my very rough calculations that you can achieve
around 3 kW for half an hour of flight, for $5000 and 5 kg of
batteries. Is this an unrealistic base line for me to use, before
adding the weight of battery heat insulation and other things?