Buy a factory 40X. Save a little money or if you can get it less than your budget, buy a jewel trigger. Save some money and buy a stock. Save some money and if it doesn't shoot to your satifaction, have it rebarreled to a custome BR barrel. Add a tuner and you have as good as most anyone...a little at a time.
The clasifieds on this site is a place to start. The gunbrokers, auction arms, etc. Lots of CMP guns on the streets, some without bolts. If you can get one of those at the right price, Pacific tool now makes a replacement bolt.
Check the classified ads on this site periodically. Also, attend some ARA or other sanctioned matches--sometimes participants still have the rifles they started out with. Check GunBroker.com or AuctionArms.com. Check your local gun shops. Don't limit yourself to a Remington 40X, although they're probably the easiest to upgrade with trigger and stock. You might find a good Winchester 52C or D, or maybe an older Anschutz with a 54 action. Hope the above helps.
You should go to a match. Look around, see what is winning, ask questions, if you act right, they will let you shoot. Get all the information you can before you buy anything. You will be money ahead to buy used... and shoot it first.