In some areas of a design, plastic is the best material choice. For instance, the fuel tank, as plastic doesn't rust. With some components that take a beating, plastic can take the hit, deform and bounce back, where metal, bent forever and possibly damaging other components in the process. This sure is the case for the discharge chute on my mower deck.
As for the adjustability of the mower deck, I'd be more concerned with the range of height over the number of positions.
The reason for the pricing without a mower is, there is in all likelihood more than one mower deck available.
The 2xxx series Cubs are a decent mid-line model. I like and prefer a horiz engine and with that the possibility of a shaft drive for the trans. I also believe with the 2xxxx machines you also get a decent cast iron rear axle with serviceable components.
The 2xxx series machines are a lot like the legendary 3xx series Deere's in that they use horiz engines, shaft drive and use a belt drive for the mower. The Deere's had some hyd for the implements. Have to go to the 3xxx series Cubs to get the hyd but in addition with the Cub you get shaft drive for the mower as well.
When shopping look beyond the price tag and advertised HP. For me engine HP is the last thing I'd be concerned over. Compare components between brands. Is there a weight difference between brands and can you see where the weight difference is. What kind of bearings do you find and where. Even check linkage, is it just metal to metal or is there some kind of bearing/bushing being used at connections. How does it fit you? Do you prefer sealed bearings over ones that can be greased? Where are you willing to trade off one item Vs another. How would you judge fit/finish Vs heavier components and more bearing/bushings at wear points? If you are going to do your own service, how easy is access to those things you need to get to. How is dealer service between the various brands.
Lots of things to give serious consideration to that doesn't stand out in the showroom as the shinny new finish and color do.
I spent several weeks making my decision, even having the dealer bring one out to the house to see how it performed on MY property. That was a real benefit as I had to go with another mower deck design that would work for me. I've lived with my decision for 8 yrs now and have no regrets. If I had made a decision in an afternoon's looking, I suspect I'd not be as satisfied as I am now.