This seems to be a post about buying your way out of a problem.
Invariably, it never works.
It seems a little hard and unfriendly, but if you take this advice, you will never regret it.
Persevere and get your boring sorted and you should hardly ever need to buy a very expensive reamer.
You are working with cast iron, and that is one of the easiest materials to machine, if you can't bore that, you won't be able to bore hardly anything.
Rigidity and tool tip alignment is the secret to boring, get those right and you are 90% there, the rest is just finding a good speed for the job and getting your feed right, if in doubt, slow down both the lathe and feed and take small cuts.
Drill your job out to 1/2" then you have loads to practice on before you get anywhere near the size you need.
BTW, on a cylinder, usually near enough is good enough, as you make the piston later to match the bore, so if it is a couple of thou over or under on your bore, you should have no problems. Also, if you are boring right the way through, don't tighten up your chuck jaws too much otherwise you will end up with a triangular or square shaped bore where it has been held in the chuck, in fact the same will happen if you use a reamer or not. I always try to bore critical dimensions on the material outside the jaws and then part off.
Sorry to be so hard, and have a look at my signature line.
John