HI,
before you get a new starter climb under the car and try to turn the engine by hand (be careful to disconnect the ignition BEFORE you start! This is not to start the engine, but if you can't turn your engine by hand most likely it isn't the starter being duff, but your bearings gone/too little oil/something fried in your engine. Engines should be turnable by hand, with a bit of force, but smoothly turnable. (just grab the flexplate with gloves and wrench it round.) My 350 has a 240 amp Battery, turns just fine, but compressions only about 9:1.

THINGS THAT CAN BE WRONG IF THE ENGINE DOESN'T TURN ON THE STARTER:

1) startergears worn (you'd hear grinding noises)
2) starter not properly aligned (not likely)
3) battery dead or old
4) poor connection/ too thin cable between bat and starter (don't forget the negative cable HAS to go to a GOOD Engine ground! I.e. Exhaust manifold, a block-bolt,...
5) Battery and/or starter terminals corroded
6) Engine at fault (see above)
7) starter old, not lubed enough, gunged up

I would check these things first, before you spend your money on a new starter. Otherwise you buy a new starter and it was only battery terminals that needed cleaning, your out 200 bucks, feel like an idiot and it didn't improve a thing. Check it out.