I think a good "intro" gas engine is the Brison/FPE/Taurus 3.2.
I think a good "intro" gas airframe is any of the Wildhare 50cc airframes.
For the budget minded person.
The Blackhorse Cap 232 1.80 for $199 shipped from Hobby People.
http://www.hobbypeople.net/gallery/159524.asp
The DL50 engine for $370 shipped from Valley View RC.
http://www.valleyviewrc.com