With EDF's, the size of the plane determines the size of the fan unit that will propel it. There are no real "standard" sizes, but most "micro" planes use around a 50mm fan. The L-39 uses the hyperflow fan, which is about 55mm, if memory serves. Kyosho makes a few small EDF planes that use a 54mm fan. The down side is that they're small planes. The up side is that you can get them flying for very little. ESC's in the 25 amp range, batteries usually smaller than 1500 3s, 4s if you really want a hot setup. I had my Illusion flying for about $300, not including the price of the airplane.

The Sportjet is a great flying airplane, but it's a 70mm fan. I went fairly cheap and low power with my setup, HET 2w 20 motor and a Phoenix 56 speed controller, with a 3200 3s battery. That set me back about $260 or so, but I already had servos, receiver and some other bits and pieces. I got a plane that could be handlaunched and landed on grass, but had a decent turn of speed. I've seen these planes set up with 80 amp speed controllers flying off 5s, a hot setup puts 700+ watts out the tailpipe.

Propjet versus EDF.... you'll get more instantenous acceleration and thrust out of the prop, and they're usually cheaper to set up. But it's still a prop. You've got a prop on your jet.

Hope this helps...

Andy