I agree with you on buying the gun rather than just the barrel. Was looking for just the slug barrel but found a combo with 2 barrels at a price that was just way too good to pass on. I can ALWAYS use a new firearm, whether I need it, well that is another story.
Around here the going rate is 160+ (sabot barrels are higher) and barrels generally need to be ordered which is more of an annoyance but can be tolerated.
I have seen some sites on the web, if I recollect properly, that were less than 200 so you may want to try that route. Mossberg also makes barrels for the Remington though you would need to check and see which ones they actually offer.
Manufacturing costs can vary but retail prices are generally set as to what the market will bear or to achieve certain marketing goals among other things rather than the actual manufacturing cost itself. Can't fault the manufacturers for wanting to make a profit, it is the reason they exist in the first place. About the best one can hope for is that a sufficient number of competitors emerge to bring the price down.