If you've never done it before I'd start with a stock gun that you're comfortable with, doesn't much matter which (preferably your carry piece or something similar), and get some experience then decide if you really need a full on custom job to be competitive. A lot of these matches, particularly local club shoots, are won or lost on the draw and on reloads because that's where people often fumble, it's hard to make up time no matter how accurate you are if you've got poor gun handling skills. Work on your basic skills and get familiar with the game first then upgrade your gear as appropriate for your needs.
“Never give in. Never give in. Never, never, never, never—in nothing, great or small, large or petty—never give in, except to convictions of honour and good sense. Never yield to force. Never yield to the apparently overwhelming might of the enemy.”