I have a 2000 Ford explorer sport. 2 door. 2x4. 5 speed. 4.0. I would love to swap in a v8. What would it entail, and how much would it cost?

First, check and see if a different transmission was used in the V-8. That will be a deal breaker if you have to do the swap. Easy enough to check on-line. Purchasing a remanufactured engine usually does not come with valve covers, intake manifold, oil pan, water pump, etc., so that is an added expense there. If the old PCM can be used, then someone will have to update it (if possible) or you'll have to purchase one new. Then there is wiring to be considered. Cost? it can be up there, inasmuch as trying to find a used engine is "iffie" in my opinion. I replaced a v-6 engine in a 2003 explorer with a remanufactured v-6 engine from a national retailer with a 100K warranty for 3500 bucks. You can use that figure for a basis once you begin shopping around.