The DelSol must have had an Auto version then cause I'm 90% sure the '99-'00 Si wasn't auto.

Is it a B16A2 or B16A3?

Do a google search for B16A and see what the shops are selling them for.

I wouldn't buy a motor off of Ebay. You will regret it I assure you.

I don't remember what sites sell them. I'm pretty sure that one of our sponsors does... http://www.japandomesticmotor.com/