Need some help

Alright, so here's my situation. I have an opportunity to purchase a NIB S&W M&P15 in 223/5.56. Due to a promotion S&W is running, if I make this purchase before Dec. 31, I also get 5 free 30-round magazines. My cost, paying cash, would be $891, tax and background check included.

Here's the catch - in order to get it, I would have to sell the first two guns I ever bought, a Rossi 223 with a 20 ga exchange barrel, and a Springfield M6 Scout in 22lr/410. Both of these guns are single shot. I do not own a semi-auto rifle, and my only other rifle is a Mosin M38 Carbine.

So, thoughts and some input on what I should do?