To get 18650 Cell Price down to where it might be worth it if you Build your own Packs, you have to Buy 20,000 Bulk then you get them for $1 each. $5-$6 is the norm I found at the local Battery Stores. The Lazair was a Motor Glider Ultralight that flew on 18.8hp, the majority of Legal Part 103's need 25-35hp. For now, the FAA says Battery Weight is included in Total Airframe 254lb Weight. So till you figure out How much Weight you have to use for each Airframe, it's a moot point. Most of these Airframe Manufacturers haven't done any Test with these different Gas Engines. probably the Top (2) today, the Pheonix 103 with a Hirth F-23 (50hp) Weight: 78lbs, including reduction unit, full exhaust, and electric start or71lbs with recoil start reduction unit and full exhaust. 254lbs - 78lbs = 176lbs for Airframe. The Aerolite 103 just says Empty Weight (1) 235 lbs. 28 hp. - 50 hp. Doesn't Specify Weight with which Engine. The F-33 28hp. Weight: 35 lbs including exhaust sys. - 40 lbs W/re-drive - 45 lbs W/elec. start. 235 lbs - 45 lbs = 190 lbs for Airframe. So the most your going to have for Motor & Battery Packs is probably 78lbs. Which I doubt will give you even 1 hr of Flight.