Throttlebodies??

Hi there! Im building EFI 340 in the future and im collecting parts for it, I´ve been looking throttlebodys from ebay, summit, jegs etc. but I really dont know whats the difference between a 300$ an 800$ part? Bet 1000cfm is enough but theres more than a few options, please help me out. This is what I have found:
https://www.summitracing.com/int/se...efault&SortOrder=Ascending&retaillocation=int