89 crx swap question

I have a 89 Crx Si and I want to do a swap. My question is, what is the best motor that will bolt right in and what is the most cost efficient way? Please Help

i would say (in my own opinion) a single cam zc. for a drop in it's good. anyone else???

Thanks for the respones, my next question is. What hard ware is all need to complete the swap?