It sounds like you like the deal, so I say go for it. Worst case scenerio you wind up a couple hundred behind to get what you want when you want it, and in my opinion that's okay. Same reason it's okay to spend $20 for a beer and a hotdog at a baseball game. Plus, you avoid all the pita of dealing with selling a gun on the internet. The dealer gets a couple of guns that with some work he can make money on, and you get a gun you want. Everyone wins.
It's your money, and I'm not going to tell you not to use it to get the stuff you want.
si vis pacem para bellum