OK, so I started with a snide remark. I apologize. So, FRJ, if you want to build a Barn gun, poor boy, or schimmel. Here's what I would suggest, assuming you wish to get the best for your buck. Give Troy Roope a call at Stonewall Creek Outfitters. He can set you up with a .32 to .40 cal. 3/4" barreled Rayle barrel for $140, and breech it for you for an extra $20. For about $150 he can get you a nice precarve in Southern Mountain, or Tennessee, and for less than $135 a nice late Ketland Chambers lock. Small parts may add another $35 to $50. You can easily make the thimbles trigger guard, and there's a tutorial for triggers. Sights are cheap, and this site will help you along the way. Take your time and you will have a gun you will be proud to post here. You could do it for less but I don't think you will have a quality gun from some of the others at this price. If you are going flint you need a quality lock, or you will soon grow unhappy from frustration. You might even get lucky and have Troy's son decorate the shipping box for you.
Bill