As stated above, the most practical course would be to buy a Maverick 88 or similar cheapie pump gun. But if you like single shots (I do!), that alone is a good enough reason to get one...or two...or...
Up until a couple years ago, the H&R singles would be the obvious answer, but since H&R shut down the existing ones apparently transformed into solid gold, so you'd need to be lucky to find one in your range. I have a Turkish single, one of the goofy folding ones, that comes threaded for chokes and it's a fun gun. A set of stick-on fibre optic front/rear sights, a tight full choke (I actually use a turkey choke in mine), some #9's and you have the ultimate backyard House Sparrow gun. And, of course, there are all those old Cooeys and Rangers and others on the EE.
I recently got a brand new Stevens 301 12-gauge hammer single and am pretty impressed with it for the money (about $300). Light, handy, threaded for Winchokes, tool-less takedown, very decent trigger. It's like a Chinese-made H&R, but with the addition of a manual stupidity...er, safety...on the left side. It's become my
long-range backyard House Sparrow gun.
The 301 that I got has a little mini pic-rail mounted on it that makes mounting a red-dot easy, although sadly the rail is a bit out-of-spec and doesn't support all red dot mounts properly. But I got one on there, and the little single excels at allowing you to use all kinds of adaptors to shoot .410's, rimfires, handgun ammo, etc...another advantage of single shots.