Couple things to consider, I recall the first hotwater heat system we decided to keep, boiler was newer, appeared in
good condition, wanted to save some money. But when we tested the system water lines were busted everywhere apparently
not to well winterized, after two weeks and two different heating contractors about 4,000 later it was up and running.
For the next five years I always replaced them with a central system heat and air. This summer I bought one with hotwater heat, . Good condition, house didnt need a lot of work decided to keep it, about 15 people through the first two weeks, two didnt like the busy street, the other 13 liked the house but not the fact it didnt have central air. 20 some people through in four weeks, ended up selling for 8k below original list. If I had central air, it would likely have had multiple offers the first week.
Our typical costs to install new central system with ductwork, high efficiency furnace, central air is under 6k, most convoluted system to date cost us 6,500 some. We have done at least 10 in the last 5 years, I wont put another house on the market without central air, your market may be different. But here anything over 100k I would not put on the market without central air.,