For .303, I use Sierra 125gr Spitzers (make sure you get .311", not .308"), new Winchester brass and primers, and 45gr of Reloder 15. This is a stout load, just below max, and your Enfield may not be able to handle it. This is *not* my plinking load, BTW; this is for serious work.
I pay ~$11 for 100 bullets at my local shop. You should be able to get a better deal from Midway (http://www.midwayusa.com).
Final note: this really should be in the Loading forum.
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