It should be both cheaper and allow you to do more if you do it yourself. First and foremost you want to make sure the engine you get is as healthy as possible. Check the oil, it can be dark but shouldn't have water in it, if it's like a milk shake or chunky probably walk away. But you may not have many options, so just keep track of what's available as you hunt.

A battery and the tools needed to check compression, possibly leak down but definitely compression, as long as it's consistent across the board I wouldn't worry about it being especially low so long as it's not way below minimum, being in a junkyard it won't likely show the same numbers you would see if it drove in off the road. So consistency is the ideal. If you can drop the pan and check for rod play that might be worthwhile.

Once you have a solid engine, you have the ideal opportunity to reseal every external gasket, grant seals, oil filter/cooler adapter etc. Clean it up and even paint it if you feel like it. Nothing wild, but a clean and painted engine makes future maintenance so much nicer.

Same goes for everything you have removed for the swap. Clean up the accessories and brackets, replace or reseal leaking things like power steering pumps, the transmission seals, axle boots etc.

Clean the engine bay, touch up paint, clean and paint brackets, deal with rust and such.

If you are doing all this at once and the cost looks intimidating, keep in mind that many things often replace can be rebuilt instead. It might not make sense to rebuild your power steering pump if it's gone out on a Monday and you just want to get back on the road, but in this case $10-15 for a kit and some labor on your part can save you $100+ on a likely cheap and dodgy rebuilt part from the store. Multiply that by all the things you could be working on and you can easily save hundreds or thousands by refurbishing things yourself. And you learn a lot along the way and build confidence.