I really like the CRRC Pro GF26i v2 on my Carl Goldberg Wild Stick 120. I use a 17x7 APC prop. The 26cc electronic ignition engine is around $200 shipped via Valley View RC. Easy break in, easy starting, good power, excellent transition between idle and full power. Mine is a side-mounted carb, so if you don't mind carving your cowl a bit (Wild Stick does use a cowl), a pretty good choice. Very economical to operate. A DLE20 or a DLE30 would also be an interesting choice. I have the DLE30 already and a DLE20 on order.

But the CRRC Pro GF26i v2 was an easy first gas engine for me.