Well first of all, no centerfire is going to be as cheap to shoot as a .223, especially one that throws 286 gr bullets. Material costs alone are obviously going to make the 9.3 more expensive to shoot, that said, it will also be far more potent than any .223 round.
Swaging .375 bullets down to .366 is one thing because you are basically forcing a larger bullet (.375) through a bullet sizing die in order to extrude it to a smaller diameter (.366). Your only real concerns here would be ensuring that your final diameter was appropriate to your bore, and that the lead core and copper jacket have had a similar amount of spring-back.... which they don't but it seems like lots of folks have done it successfully, so maybe its not too big of a deal.
As for using a .357 bullet in a 9.3, that idea
will not work. even if you crimp a .357 bullet into a 9.3 case, the bullet will still be too small for the rifle's bore. At the very least this will result in a slow load with poor accuracy, but it could also lead to a dangerous situation. Basically, this idea is a no go, but if you really want to shoot .357 bullets in a rifle, why not just get a 35 Whelen? The Whelen would allow you to do exactly what you're describing here.
These are the cheapest bullets made for the 9.3, and should work fine for hogs.
http://www.grafs.com/retail/catalog/product/productId/12622
Although they are currently out of stock, Grafs usually has them available, and I imagine they will be back in stock before too long.
Additionally, if you really want an american made bullet, the speer is the most affordable in this caliber.
http://www.grafs.com/retail/catalog/product/productId/17300
Here's a link to a post from a guy that's swaging 375 to 9.3, it seems like there is a little machining involved in opening up the dies.
http://forums.gunboards.com/showthread.php?28733-Swaging-375-s-to-9-3mm
If all of this is still too expensive, you might want to consider sticking with .223, or maybe giving .308 a try.