I really wanted an underhammer and was looking to make one even. The H&A from what I have found are pretty decent quality. I do have a place where you can buy the locks and the lock itself is about $150. A barrel runs about $125 for a Green Mountain or $200 for a Colerain. I found the cheapest stocks set up for this style rifle in partially finished form for $120. So if you really want one, you will be spending this plus some for sights, barrel tenons, ramrod hangers etc. All said about the cheapest I could make one was $800 or if I made my own stock from scratch, about $600. If you can get one for a decent price, $300 would be a good average depending on the bore quality and overall shape. I'm not a shop owner, but had looked for some time into this myself.