Yes, Schoolboy, one could get a rifled barrel and sabot slugs for around $140.....but NOT for a Benelli Nova - which is what houtsdg said that he has. Barrels for Benellis are NOT available that cheaply. So, your suggestion, though valid for a Mossberg and perhaps a Remington....is irrelevant, so far as a Benelli is concerned.

houtsdg,
If you are not yet certain that you wish to invest in a dedicated slug barrel, whether rifled or smoothbore, then why not try good "rifled" slugs in your standard Benelli barrel ? This will give you some experience with slugs....at a tiny fraction of the cost of dedicated equipment. Yes, a full-length barrel is a bit more unwieldy than a short slug barrel....but not so much to be unpleasant to shoot - especially in Iowa cornfields. A good slug to try would be the Brenneke KO slugs (NOT sabots). The work very well in smooth barrels...and are pretty accurate (3" or less at 50 yards). Ordinary "rifled" slugs are less accurate, in my experience. The Brennekes are not expensive, either. Use a cylinder bore choke tube or a skeet tube (as little choke as possible) with these slugs.
If you want better sights than the standard bead....aftermarket sights which attach to the vent rib are widely available....and cheap.

If you do absolutely want a dedicated slug "rig"....then I would suggest getting a pump shotgun already equipped with a slug barrel. This could cost less than a new rifled Benelli barrel...and be a better proposition for field use. If you decide that you want a rifled barrel, then you can often buy a Rem. or Mossberg pump gun already equipped as such....for less than buying the barrel separately.