Hey there, I looked at your profile and saw that you already have the katana, knuckles, and Mines. looks like you enjoy the melee part of the game :)
to put it shortly; The revolver is the single BEST purchase you can make right now. Nothing else comes close.
If you want more details, read on: when buying weapons, you want to consider how much you can earn back with each purchase you make. This means picking the strongest weapons for the lowest cost. The UMP and Sniper are two of the best guns in the game, so you can use either one in your primary weapon slot. You have trap mines, which are slightly worse than M67 grenades, but are still very helpful if you place them in smart locations. This only leaves your secondary weapon, and the USP that you get for free is garbage. It's damage and ammo capacity are pathetic. The revolver, on the other hand is borderline OP. It's stronger than some primary weapons. Buying the revolver will substantially increase your damage, which will allow you to earn XP faster an purchase more weapons. Definitely buy it as soon as you're able to. Hopefully this was helpful!
Hey there, I looked at your profile and saw that you already have the katana, knuckles, and Mines. looks like you enjoy the melee part of the game :)