Here's another option you might start looking into. Thrift stores. I know several of the thrift stores here in our area get large aquariums from time to time, and typically sell them off for a lot less than you'd pay for a new one. Since you're not worried about putting fish in one, it won't matter if it has a small leak anywhere, or if there is a small crack on the glass somewhere. Just know the prices of the new ones before you start looking, as some thrift stores have an overblown idea of what their stuff is worth. However, since you're talking about not absolutely needing it until the end of the year, you have plenty of time to start watching for a good deal on one.
Check the classifieds as well. Often, people are cleaning out their garages or storage units, and decide they no longer want to store that big old aquarium they had. Same caveat: know what you'd pay for a new one first.
Any used enclosure you might buy, be sure to take some time to clean out and disinfect before using. Swabbing out the inside with bleach will kill just about any bacteria or germs that might be residing on the surfaces (straight bleach was found to be about the only thing that would kill the Corona virus on the surfaces of dog kennels), then of course, wash and rinse well to remove any residual bleach. Allowing to air dry afterwards in full sunlight is also helpful, as many microbial lifeforms are highly intolerant of the UV rays of the Sun. Not that there should be any left after the bleach, but what the heck. Sunlight is free and easy to use.