Anything stored in a shed should probably have something covering the barrel ends to keep bugs from building a nest in the barrel or barrels. Would suck to need your firearm and check for obstructions and find a wasp nest or whatever. My luck it would be the mud daubber wasps.
I would try like heck to put together an ar for 450 or less. Kind of depends on your shipping and transfer costs if lowers are expensive for you to get. Watch the psa emails and get a cheap parts kit. No it is not an awesome ar, but right now is the time for an ar to wind up anywhere you want one. To some extent I would just snag a few mags and some ammo I already had to make the budget. Still gets me how most cheap ar parts kits don't come with a rear site, but I got some carry handle sites cheap so I don't care anymore. I know some people can do the cheap ar for 400 or less, the slickside kit is the only way I could have done it. And I guess in some areas an ar won't fly.
I am not knocking the shotguns, I have some shotguns and for the right price I will buy older shotguns even if they are not in nice shape. Bamashooter has some threads on the police trade in parts kits to turn your shotgun into something more "tactical" if that is what you want.
I have also been considering some of the s&w police trade in 38 specials cause they have no lock and are older assemblies that seem nicer than some of today's stuff, and I don't care if the finish looks worn. Function. So far I have held off because 300 out the door seems to be my price and everything is more like 400 out the door that I run into.
Heck, see if anyone has a rusty ak in their trash cans they want to get rid of. A bit of oil and it will probably work and I kind of like my abused ak stuff because it keeps me from trying to sell it for today's higher prices.