Good Cheep Tatical Guns?

i just saw a Finnish M31 Suomi 9mm going for 400 dolalrs on sale from 550. I could have it shiped to my town and tax would run up to around 500 dolalrs. I love the look of them and they take 71 drum bags that only cost 30 bucks. Id buy a bunch of drums and stick bags. probally about 5 drugs and 5 stick mags. Is this a worthy gun. Id be selling my SKS with all its tatical gear ot buy this new rifle. Im wondering what gun should i buy that will be cheep (500 ) dollars and under and that will take magazines that hold 20 plus rounds. I want a gun that could hold alot of rounds, fire fast, and the bullets and clips at a decent price. Im thinking of AK47 but i love the Finnish M31 Suomi 9mm . give me advice guys. Im trying to get a powerful gun collection going. so far i got 2 mosin nagants, Yugo SKS, 9mm Hi Point, and will soon have a 1800's bot action swiss 43 caliber rifle and a 12 guage noble pump, 20 guage sing shot, 410 single shot.