First i want to say there is no question, the LE is a wonderful machine and a totally different thing than the SD1.
But i want to fly a little bit faster than LE and similar planes. Im thinking about to use a faster airfoil for the LE so the cruising speed raise to about 80 mph. I know it needs some stronger building.
I saw a J3 Kitten Reliant build in Italy, empty weight 395 pounds, with Rotax 582, cruise speed 85 mph, VNE 100 mph, spoke with owner and he said there where never signs of flutter.
i dont know if that is possible with the original airfoil Goettingen 387, see here: http://airfoiltools.com/airfoil/details?airfoil=goe387-il
I had the opportunity at Friedrichshafen 3 years ago to see the plane live, the german seller was there with his own SD1.
I think building it from plans compared to a LE probably takes 150-200 hours more but not cost expansive.
This is only a european (Germany) phenomenon because the admission rules are very strict and you need perfect soldered metal pieces and so on...
I live in italy and there is not so strong to meet the admission.
Anyway i think it depends of your building skill and what you can do it yourself.
Probably i can built it with 500 bucks more than a LE.