For that matter, it's not hard to learn to cut entirely new panes for old-school windows, and the tools aren't particularly expensive. Break a modern window and you'll most likely be replacing the whole thing, frame, casing(!), and all—the entire old window becomes trash.
... however, I do prefer the modern ones, myself. Energy loss through single-pane windows is no joke.
The seal between the pane and the wood is usually glazing. If that’s failing, you need to replace it. You can buy glazing putty at a big box store, and see how to do it on YouTube. With a little practice, it’s about ten minutes/window. $15 in materials will do a dozen or so.
If it’s leaking between the wood, you need to caulk. That’s $3-$13 in materials/tools (depending on if you already have the gun) and a couple minutes labor.
You may also need some flashing over the top to direct the water away from the pane. This is slightly more complicated. Probably $30 and an hour or so.
If you don’t want to learn these skills, a handyman should be up to any of them.
Multi pane windows also need to be flashed and caulked, just like your single pane. The only piece that I mentioned that is different is the glazing. Glazing can be replaced, the interior seal on a multi-pane window cannot