Yea, there is a lot of price variance. Among the three options I identified, the second one is most attractive price-wise.Usually if you order a remanned engine the company has local installers they deal with. It allows you to keep any warranty as well.
You might want to look at your budget before doing anything. The engines you've mentioned vary widely price wise.
I have looked at 4.6s on eBay, eighty6gt. Some appear like they could be good options. I have just never used eBay for a purchase so large. What does “LKQ” mean?