I loved Supernatural when I was doing straight hydro. It's a dry nute, so you don't have to pay to ship the water as in liquid nutrients. It's a little pricey at hydro shops depending on your area, I think I paid $30 for 400 g. But it's ~$10-$15 for 400 grams online and you only need 5-7 grams per gallon. So on the low side it should make around 80 gallons worth. That's about $0.20 a gallon, or $0.30 a gallon at full strength (I would recommend starting at 1/3 strength, shits pretty potent)
This is got me wondering, which brand provides the most nutrient solution per dollar... it might be time to make a spreadsheet