I don't know a lot about steel boats, is there a such thing as a moderate displacement steel hull, or are they pretty much all heavy displacement?
I saw a 24 foot steel boat that weighed 9,000 lbs. with a go-fast tall rig this winter. Yes, that's heavy displacement, but it shouldn't hold it back. The concept of "heavy displacement" is a moving target as all boats have tended to get lighter over the years. But my steel 41' cruiser is 24,000 lbs. and a Catalina 42 is nearly 20,000, so I'm "moderate" for steel, and the Catalina is "moderate" for fibreglass.
Or am I a little skewed in thinking that larger displacement boats tend to require more effort when singlehanding?
That depends on hull shape, sail set and area and a few other factors. Some boats are "driven" easily in that they track well and have a "kindly" motion (non-puke-producing) in a seaway. Others are plain fast, and frequently squirrelly in that they are "tender" and must be actively sailed. If you are going to cross oceans solo or with one crew, you would tend to gravitate to the "slow but steady" type of boat that can largely steer itself and has a more modest sail area. All boats should do their hull speed in 25 knots: a lighter boat will do it in 14 knots, while the heavy one will want 20. Ease of use on the ocean means less time on deck reefing and shaking out, meaning you want to keep up a full hoist as long as you can. That and tankage/stowage argues for a more commodious boat....particularly in your price range.
And I guess I should have stated from the outset that my purchase budget is around 80k total (fitting included) and I'm hoping to come in well under that but I could stretch for "the right boat"
Yachtworld.com is your friend. Simply alter your parameters and consult books like "Desirable and Undesirable Characteristics of Offshore Yachts" and "Heavy Weather Sailing", as it's a Good Old Boat, rather than a new "hot rod", that is most likely in your future.