just go with the 2.4L that came in the z24 and even some base cavis. or you could swap a 2.2 ecotec into your car, or go crazy and do a 3800 SC swap.
But i would go with the 2.4 swap, with a 5speed. the 2.4 came in the grand am,mailibu, alero, sunfire, cavi, and so on. you could get a fresh one for like 2 grand and a tranny for 1500. or a used one from a yard for maybe 900 for the motor and 500 or so for the trans. check out
www.car-parts.com