Take a look at the Chiappa M4-22 (they spell it mfour-22 if you're googling it), cheap and cheerful but still AR-format not a dress-up like the Mossberg and shoots well. I've got one I picked up from Classicfirearms for $249.99 for the complete rifle. You do really need a standard AR buffer tube and collapsible stock to put on it, 2 min job and I had them in my parts bin, the standard molded non-adjustable fake MOE thing is utter garbage. Once that's done it's a perfectly good plinker IMO, don't expect M&P 15-22 quality though obviously. The upper also fits on a standard lower if you want to use it on your current lower.

If you don't want to wait for a sale, you can get them at Bud's gun shop for a shade over $280 right now. Or you can pick up just the upper for just around $200. Btw I have the gen 1, the gen2 is a bit more money but looks a lot fancier in the pictures, never seen one in the flesh.

Decent overview of one here: Chiappa m four 22 Review @ Trigger Happy - YouTube