Replacing 1880s basement windows
If the framing around the window is essentially intact, insert replacement windows are fairly cheap and fairly easy, though you'll lose some glass area.. If the framing is rotting you'll need to deal with that; in that case either inserts or completely new framed windows may be the right choice. For the latter, make sure you install them with proper flashing &amp; water barriers.

If you can't afford to replace the windows, all you can do is try to patch things well enough to not leak too badly and not fall apart. I have one basement window that I have temporarily just slapped a sheet of plexiglass across, held in place with caulking.... temporary ugly kluge but it does seal the opening better.