You are correct, his name is Lenard. Value depends greatly on who assembled it and what barrels were used.
I have one in flint, and from what I understand, most of these left his shop as just actions. It was up to the gun builder to barrel and stock the action. Every one I've seen had "L. Day" on the sideplate, whether they were assemble as a complete rifle or not, so it can be impossible to tell who built the complete gun unless the barrels are signed or there are some other maker's mark somewhere.
All that said, there's just no way to put a value on it sight unseen, and tough to do even when seen sometimes. There's just too many variables, and as I indicated earlier today, many's the 'smith who's turned several hundred dollars in parts into a gun worth little or nothing.
Another thing to consider on non-production/custom guns is that they are only worth what a buyer is willing to pay and the seller willing to accept. If someone really wants it he likely better buy it as he may never have an opportunity to buy it again. It all comes down to the price that satisfies both parties as there's no Blue Book for this type of thing.
Enjoy, J.D.
