Reese Surplus has (or at least had) some wood BM-59 type folding stocks that had a wood pistol grip. They were quite reasonably priced. Around $120 or so. Repros, but decent. Finding an original BM-59 stock assembly fitted for an M-14 (as sold by Springfield Armory many years ago) is going to be next to impossible. Expect to pay at least $350.00. You will need to bed the action.
Springfield Armory used to sell a synthetic folding stock with pistol grip (I believe it was made by Choate Machine & Tool), but they have been out of stock for years now. The stock used to sell for about $250.00 from the factory. They come up for sale on auction sites (gunbroker.com or eBay) from time to time.
For around $250-$300, you should be able to pick up a used E-2 pistol grip stock (also wood) from Fred's. It will probably need to be bedded.
The new manufacture synthetic or alloy stocks with pistol grips (e.g., Sage Intl) are all extremely expensive, although they do offer the advantage that they do not have to be "bedded", are not affected by weather, and have integrated rails for mounting stuff.