The 2037 is one of the most common Postwar steamers out there I'd say. They were sort of the midlevel postwar engines since they were die cast, had all the features such as light, smoke, 3 position E-unit and sometimes a whistle, but headed up mainly more basic lower end train sets. Lionel produced them starting in 1953 and made them through 1963. According to my David Doyle book, 1956 was the only year the 2037 wasn't produced. They generally came with the boxy Santa Fe style tender either with or without a whistle although a couple of other non-whistle tenders were also used. The one behind yours would not be correct for a 2037, although it's probably worth about as much as the locomotive by itself. Most recently sold listings for 2037 locomotives with no tender are in the $40-50 range and slightly more with the proper tender.
Although not really overly rare, the 2056 Hudson is unique in that it was produced in 1952 only. Due to the Korean War, Lionel could not get the materials used produce the magnetraction feature, so the 2046 was renumbered 2056 and produced without. They would have come with the 2046W Lionel Lines streamlined whistle tenders. The average sold price on eBay I'm seeing is right around $100 give or take. Some in great condition with locomotive, tender and all the boxes have gone north of $200.
Ebay's "Sold Listings" filter is a great tool for getting a general idea of what certain items are actually selling for, vs what people are asking.
I think Bill's prices are about right. Postwar doesn't bring what it used to unless its truely mint in the original box. 2056 might have more appeal to collectors vs operators as it lacks magnetraction but also less common.