Best to start with something simple that's not a weapon and work your way up. Building a battlebot wrong could kill you. Might I suggest a simple wedge first? and a tiny battlebot at that?
It sounds like you haven't built a single robot in your life before (I am also suspicous if you have ever built anything before). So your best bet if you want your first robot to be a combat robot is to build a SOZbot. They are tiny battlebots that are cheap, and have more killing power for their size (due to the fact they are so cheap they sacrifice armor for weapons).
http://www.sozbots.com/
http://www.battlekits.com/ has their featherweight kit which is practically complete with everything a beginner probably couldn't build themselves. Good if you want to build a full-size battlebot as your first (but highly NOT recommended if you've never built a single robot before of any kind).
And for parts for combat robots of all sizes:
www.robotcombat.com
They also have starter packages for full-scale battlebots (though not as nice or as complete or as cheap as the BattleKits featherweight robot.) They also have SOZbot starter kits which are by FAR your best bet.
A wedge or lifter is probably safest and best for now (and cheapest!) Don't use drills, hammers, or saws- they are usually all show no damage (ever tried to drill or saw through metal when it's just sitting there and clamped? imagine doing that when it's unclamped, moving around, and attacking you). My preference is spinners, flippers, and crushers- you know the kinds of robots that actually do harm to other robots...and kill you if you build them wrong. So a wedge is definately the best full-size choice for you or a slightly fancier SOZbot.
Hope you got lots of money...if not your only choice is a SOZbot.