There are plenty of good choices completely dependent on what you want/need it for. You have a 1911 so a full size range gun is covered. I have 100% confidence in my High Point 9mm that was less than $100 used when I got it and they are available for around $200 NIB today. Awesome, ugly, heavy gun but mine will go bang every time and is fun to shoot.
Got a .22? At Academy for $300 you can get a NIB Heritage with a .22 mag cylinder and have $100 left over to buy some ammo. Awesome plinker for the money. In semis there are a few decent guns available at that price. You may be able to buy a .22 conversion for your 1911 at that price but I have not looked at that personally.
You don't have a carry permit but there are several pocket .380s that come to mind. The KT P3AT is a good gun for the price as is the Diamondback but make sure you get a new Diamondback as the quality on the original guns was pretty bad. I think the Ruger may be a bit north of $300 but it is a good gun. Both KT and DB make pocket 9mms in the $300 range too.
Just about any name brand revolver that you can buy under $300, assuming it is in decent shape, will bring you a lot of fun. Charter Arms has some nice guns, new and old, but do the research to make sure you get one made at the right time due to ownership changes. Mine is a great little snubbie made, I think, in the 60s but I would have to look that up. I personally like .357 because it allows me to shoot both .38 and .357 rounds.
Or you can buy 600 rounds of ammo for your 1911.
No matter what course you take it is a good problem to have. I have the itch right now and am looking for a compact 1911 because...well, just because.