At what price do they give the new owner a steel MSH? I honestly don't know. I was out of guns for about ten years, went to a guns show and bought a nice looking stainless Colt. But I didn't look it over good enough, when I got it home I was shocked as heck to find that the MSH was some kind of plastic they colored to look like stainless. Within a few days it had a stainless housing, but that was an eye opener for me about Colt.
The same general price point, depends on what model you choose. The XSE series and the 1991 series, as well as the current Gold Cup Trophy series I believe, all use flat serrated polymer mainspring housings. The Series 70 and the now out of production 1911 and 1918 repo's use steel mainspring housings.
The polymer mainspring housings are a hold-over from when the 1991 series first hit the market. When they were introduced they used a polymer mainspring housing and trigger. Colt did away with the plastic triggers years ago, but kept the mainspring housings and started using them on all their normal production guns. They work just fine.