I will treat you seriously here, your original proposal is very naive, but it may be sincere.
You are curious how a much longer cue will play, so you want to try one, nothing wrong with that. You want all the extra length to be made in the butt. Now that causes issues to start with. It is the heaviest, thickest piece of lumber, yet you want to hold it down to 15 oz. Ten inches more wood, a third more plus in length, and hold it to the same weight as a normal 29 inch butt. Hmmmmmm. Well lets assume we use a real piece of crap light wood. Will it balance and hit like we want a cue that we make in normal lengths? Will it hit with the same feel and authority? So in other words will you really be able to make an intelligent decision about the value of making a "real" cue 70 inches long? Assuming this butt is not going to be your player, only an experiment. Not likely. And a comment was made about not being able to turn a hunk of lumber that long. It is valid, Would you own a lathe a foot longer than you had to unless you happened to have it given to you, or it was a bargain you could not resist?. Ther may be someone out there that can do this, yah never know.
To cut a taper that long and hold everything true would be a huge task. I know I spent months getting my tapering system working right. Just changing my large metal lathe adjustments to cut your butt, then resetting everything back to normal is worth more than any profit from the $100 to me. Let alone knowing I made something that may split because it is light weak wood, or maybe warp because I need a year to season a long piece and cannot afford to make a " one of" like that. We season wood over years, then have to use the warpers as firewood, or inlay slabs. SO if I season a piece for you, I had better season two in case one warps. And using a rather expensive joint cuts a lot more profit out of it.
Do we have to apply a clearcoat finish to it? Well I can handle 32 inches in my spray booth, another conundrum to overcome. And if anything goes wrong when the owner of this "simple" experiment uses it under whatever conditions he exposes it to, then it is the unlucky cuemaker that must not know his craft because it was a simple job after all.
SO if you want an unseasoned hunk of light wood with a joint in it, and no decent finish on it, maybe a brushed on floor finish, and no expectation that it will not warp or crack, or even come close to feeling like a real cue should when you attempt to actually use it, yeah someone might make a very few dollars making this one of butt. But: most likely it will not play any better than putting one of those popular cue extensions on your current butt and just play with it!
I gave you a serious answer, with maybe some overtones, but serious none the less. Maybe you can better understand what you asked of for of your $100. Like I said earlier your request is quite naive, but unless you have made a cue yourself, how could your really know? SO I am not trying to disrespect you at all. Is it a gravy train and you are exposing it to the world??? OMG now that is funny. I can make more money as a greeter at WalMart. And I agree with Dickie here: Sheldon may be your man. He seems interested. It is a challenge. He may even want to throw in a case for it? Yeah, I am just ribbing him. He and Dickie are good people.
You caught me with this in the wee hours. I woke up at 545 and saw the latest responses and felt compelled to write. Hey I already lost money on this job!