I built mine starting with buying an old motor instead of using the one I had in the xj. This way I could drive my xj until I was ready to do the actual engine swap. Building a motor, any motor, is usually going to be more expensive if you piece mill it. That is the option I chose to do. If you have the machine work done and buy after market parts (cam, high volume water and oil pumps, the good gaskets (felpro), and replace the radiator, radiator fan, all ignition components, all belts and hoses, mounts, header and new exaust, everything, this is why it becomes pricey. My xj is an 89 and so everything was worn and needed replacement. I also wanted a little more than stock. Now if you buy a crate long block that is already done and you can reuse most of your factory parts and do the work yourself then yes $800 is a fiesible price.
All I was getting at is, depending on what you want, as we all know, anything can become more expensive than you may initially plan for. Not just axles, tires, wheels and suspensions. Motors are also included in this expensive hobby of ours.