I had 900 caps but I spent it on a assault rifle and a combat helmet. Firearms are very expensive, has anyone come across any free weapons while exploring? If you have then let me know where you found them.

Tons.

Everywhere.

Step 1. Find Cave
Step 2. Kill Everything in the cave
Step 3. ???
Step 4. Profit.

You should be strong enough to fight Jackels - the leader near the Nevada Hiway Patrol has a Cowboy Repeater (Winchester 73?) on her.

What guns exactly?

Hunting rifles, winchesters, rifles pretty much. No energy weapons. I killed Benny and I like using the 9mm Maria.

Well I don't know if this is what you are asking, but if you can kill deathclaws and nightkins, then head to the deathclaw nest in Quarry Junction, or Bloodbourne Cave to get an LMG, or 12.7 SMG. Also, if you go to the Silver Rush you can drag the energy weapons on the tables and shelves into the back room(without stealing, or picking them up)and once you're in the back room with your prize go ahead and steal it with no witnesses.

Yea I'll explore around there.

There is a Sniper Rifle in McCarren in one of the tents outside on top of a bunk bed it owns as a low level weapon and you can take it without stealing!

Vault 34 armory.

I don't like that place, it's scary :cryvaultboy:

What's scary about it?

If you have a high enough science (50 pts) then you can hack Contreras' terminal in Camp McCarren.
Then go to Boyd interrogating the prisoner (or if you already helped, to her office).
Report Contreras and she gives you http://fallout.wikia.com/wiki/This_Machine (M1 Garand). Or you could do Contreras' mission for it.

I've been able to one shot Deathclaws with it.

where do you find the 12.7 stuff?

Gobi sniper rifle in Snipers Nest overlooking Cottonwood Cove