The Station Cash currency that is used for the real money transactions goes on sale pretty much monthly for a day at 2x or 3x, seems the next 3x sale is on the 21st, but usually there's no notice.
Items also come up on sale, the weekly ones usually as equipment packages and individual items daily usually for about 40-60% off if bought with Station Cash. So even the top priced $7 guns could cost as little as a dollar if you spend wisely and others as little as a quarter. You can also try all the weapons before you buy for 30 minutes. Only cosmetic items are cash only.
The only downside is that earning the top end items just through playing would take an extremely long time, but that's obviously the drive for the game to earn money. I've payed $60 for games that had less good play time than this one so I don't mind dropping some cash on items.